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Atoms
Number of Followers: 1 Open Access journal ISSN (Online) 2218-2004 Published by MDPI [84 journals] |
- Atoms, Vol. 10, Pages 35: Comments on Computation of Free-Free Transitions
in Atomic Physics
Authors: Anand K. Bhatia, Joseph Sucher
First page: 35
Abstract: The amplitude T for ‘free-free’ processes such as bremsstrahlung or photoabsorption by an electron in the continuum in the presence of an external field, is usually written as the matrix element of the radiation operator taken between two continuum states. However, unlike the case when at least one of the states is bound, as in radiative transitions, electron capture or the photo-effect, this expression contains unphysical term, proportional to a delta function, and is not really the physical amplitude Tphys. We first give an a priori definition of Tphys in terms of the scattering parts of the continuum functions, which does not have this delta function term and has an obvious interpretation in terms of time-ordered diagrams. We then show that when the formal amplitude T is modified by a long-distance cutoff, the modified form Tα approaches Tphys as the cutoff is removed. The modified form may be used as the basis for calculation and approximations without the need to introduce further cutoffs at a later stage.
Citation: Atoms
PubDate: 2022-04-02
DOI: 10.3390/atoms10020035
Issue No: Vol. 10, No. 2 (2022)
- Atoms, Vol. 10, Pages 36: Hannelore Emmi Saraph (1936–2020): Her
Life in Atomic Physics
Authors: Gillian Peach, Anthony Eugene Lynas-Gray, Claudio Mendoza, Kenneth T. Taylor, Jonathan Tennyson
First page: 36
Abstract: Hannelore Emmi Saraph (Figure 1, and hereafter “Hannelore”) was an atomic physicist based at University College London [...]
Citation: Atoms
PubDate: 2022-04-06
DOI: 10.3390/atoms10020036
Issue No: Vol. 10, No. 2 (2022)
- Atoms, Vol. 10, Pages 37: Photon Emission from Hollow Ions Near Surfaces
Authors: Stephan Fritzsche
First page: 37
Abstract: Ions with multiple inner-shell vacancies frequently arise due to their interaction with different targets, such as (intense) light pulses, atoms, clusters or bulk material. They are formed, in addition, if highly charged ions approach surfaces and capture electrons at rather large distances. To explore the interaction of such hollow ions and their subsequent relaxation, photon spectra in different frequency regions have been measured and compared to calculations. To support these and related measurements, we here show within the framework of the Jena Atomic Calculator (Jac) how (additional) electrons in outer shells modify photon emission and lead to characteristic shifts in the observed spectra. Further, for highly charged Ar ions in KLm(m=1⋯8) configurations, we analyze the mean relaxation time for their stabilization into the different ground configurations. These examples demonstrate how a powerful and flexible toolbox such as Jac will be useful (and necessary) in order to model the photon and electron emission of ions as they occur not only near surfaces but also in astro-, atomic and plasma physics.
Citation: Atoms
PubDate: 2022-04-10
DOI: 10.3390/atoms10020037
Issue No: Vol. 10, No. 2 (2022)
- Atoms, Vol. 10, Pages 38: Momentum Halo in The Rayleigh Scattering by a
Bose–Einstein Condensate
Authors: Nicola Piovella
First page: 38
Abstract: A ring of radius ℏk0 in the momentum distribution of a Bose–Einstein condensate is visible when the atoms scatter a single photon. Here, we describe an approximated theory of this effect, leading to an analytic expression of the isotropic momentum scattering rate.
Citation: Atoms
PubDate: 2022-04-11
DOI: 10.3390/atoms10020038
Issue No: Vol. 10, No. 2 (2022)
- Atoms, Vol. 10, Pages 39: Measurement of Photoionization Cross-Section for
the Excited States of Atoms: A Review
Authors: Muhammad Aslam Baig
First page: 39
Abstract: A review of experimental studies of the measurement of the photoionization cross-section for the excited states of the alkali atoms, alkaline earth atoms, and rare-gas atoms is presented, with emphasis on using multi-step laser excitation, ionization, and the saturation technique. The dependence of the photoionization cross-section from different intermediate states populated in the first step and ionized in the second step are discussed, including results on the photoionization cross-sections measured above the first ionization threshold. Results based on different polarizations of the exciting and the ionizing dye lasers are also discussed. Examples are provided, illustrating the photoionization cross-sections measured using thermionic diode ion detector, atomic beam apparatus in conjunction with a time-of-flight mass spectrometer and DC/RF glow discharge cell as an optogalvanic detection.
Citation: Atoms
PubDate: 2022-04-14
DOI: 10.3390/atoms10020039
Issue No: Vol. 10, No. 2 (2022)
- Atoms, Vol. 10, Pages 40: Observation of Collisional De-Excitation
Phenomena in Plutonium
Authors: Andrea Raggio, Ilkka Pohjalainen, Iain D. Moore
First page: 40
Abstract: A program of research towards the high-resolution optical spectroscopy of actinide elements for the study of fundamental nuclear structure is currently ongoing at the IGISOL facility of the University of Jyväskylä. One aspect of this work is the development of a gas-cell-based actinide laser ion source using filament-based dispensers of long-lived actinide isotopes. We have observed prominent phenomena in the resonant laser ionization process specific to the gaseous environment of the gas cell. The development and investigation of a laser ionization scheme for plutonium atoms is reported, focusing on the effects arising from the collision-induced phenomena of plutonium atoms in helium gas. The gas-cell environment was observed to greatly reduce the sensitivity of an efficient plutonium ionization scheme developed in vacuum. This indicates competition between resonant laser excitation and collisional de-excitation by the gas atoms, which is likely being enhanced by the very high atomic level density within actinide elements.
Citation: Atoms
PubDate: 2022-04-20
DOI: 10.3390/atoms10020040
Issue No: Vol. 10, No. 2 (2022)
- Atoms, Vol. 10, Pages 41: Advancing Radiation-Detected Resonance
Ionization towards Heavier Elements and More Exotic Nuclides
Authors: Jessica Warbinek, Brankica Anđelić, Michael Block, Premaditya Chhetri, Arno Claessens, Rafael Ferrer, Francesca Giacoppo, Oliver Kaleja, Tom Kieck, EunKang Kim, Mustapha Laatiaoui, Jeremy Lantis, Andrew Mistry, Danny Münzberg, Steven Nothhelfer, Sebastian Raeder, Emmanuel Rey-Herme, Elisabeth Rickert, Jekabs Romans, Elisa Romero-Romero, Marine Vandebrouck, Piet Van Duppen, Thomas Walther
First page: 41
Abstract: RAdiation-Detected Resonance Ionization Spectroscopy (RADRIS) is a versatile method for highly sensitive laser spectroscopy studies of the heaviest actinides. Most of these nuclides need to be produced at accelerator facilities in fusion-evaporation reactions and are studied immediately after their production and separation from the primary beam due to their short half-lives and low production rates of only a few atoms per second or less. Only recently, the first laser spectroscopic investigation of nobelium (Z=102) was performed by applying the RADRIS technique in a buffer-gas-filled stopping cell at the GSI in Darmstadt, Germany. To expand this technique to other nobelium isotopes and for the search for atomic levels in the heaviest actinide element, lawrencium (Z=103), the sensitivity of the RADRIS setup needed to be further improved. Therefore, a new movable double-detector setup was developed, which enhances the overall efficiency by approximately 65% compared to the previously used single-detector setup. Further development work was performed to enable the study of longer-lived (t1/2>1 h) and shorter-lived nuclides (t1/2<1 s) with the RADRIS method. With a new rotatable multi-detector design, the long-lived isotope 254Fm (t1/2=3.2 h) becomes within reach for laser spectroscopy. Upcoming experiments will also tackle the short-lived isotope 251No (t1/2=0.8 s) by applying a newly implemented short RADRIS measurement cycle.
Citation: Atoms
PubDate: 2022-04-21
DOI: 10.3390/atoms10020041
Issue No: Vol. 10, No. 2 (2022)
- Atoms, Vol. 10, Pages 42: Update of Atomic Data for the First Three
Spectra of Actinium
Authors: Alexander Kramida
First page: 42
Abstract: The present article describes a complete reanalysis of all published data on observed spectral lines and energy levels of the first three spectra of actinium (Ac I–III). In Ac I, three previously determined energy levels have been rejected, 12 new energy levels have been found; for six previously known levels, either the J values or the energies have been revised, and the ionization energy has been redetermined with an improved accuracy. In the line list of Ac I, three previous classifications have been discarded, 16 new ones have been found, and three have been revised. In Ac II, 16 new energy levels have been established, and 36 new identifications have been found for previously observed but unclassified lines. In both Ac I and Ac II, new sets of transition probabilities have been calculated. For all three spectra, complete datasets of critically evaluated energy levels, observed lines, and transition probabilities have been constructed to serve as recommended data on these spectra.
Citation: Atoms
PubDate: 2022-04-22
DOI: 10.3390/atoms10020042
Issue No: Vol. 10, No. 2 (2022)
- Atoms, Vol. 10, Pages 43: Investigation of Electron Scattering from Vinyl
Ether and Its Isomers
Authors: Himani Tomer, Biplab Goswami, Bobby Antony
First page: 43
Abstract: This article reports a comprehensive theoretical study of electron scattering from vinyl ether and its isomers. The electron–molecule quantum collision problem is solved through a complex optical potential approach. From the solution of the Schrödinger equation corresponding to this scattering problem, various cross sections were obtained for energies from ionization threshold of target to 5 keV. To deal with the non-spherical and complex structure, a multi-center group additivity approach is used. Furthermore, geometrical screening correction is applied to compensate for the overestimation of results due to electron charge density overlap. We found an interesting correlation between maximum ionization cross section with polarizability and ionization energy of the target molecule. The fitting of the total cross section as a function of the incident electron energy is reported in this article. The correlation between the effective diameter of the target and the projectile wavelength at maximum ionization energy is also reported for vinyl ether and its isomers. The data presented here will be useful to biomedical field, mass spectrometry, and chemical database for military range applications. The cross sections are also important to model Mars’s atmosphere due to their presence in its atmosphere. The gas-kinetic radius and the van der Waals coefficients are estimated from the electron-impact total scattering cross sections. In addition, the current study predicts the presence of isomeric effects in the cross section.
Citation: Atoms
PubDate: 2022-04-24
DOI: 10.3390/atoms10020043
Issue No: Vol. 10, No. 2 (2022)
- Atoms, Vol. 10, Pages 44: Impact of Charge Migration and the
Angle-Resolved Photoionization Time Delays of the Free and Confined Atom
X@C60
Authors: Subhasish Saha, Sourav Banerjee, Jobin Jose
First page: 44
Abstract: The present study is devoted to isolate and study the effect of charge migration on the photoionization from the X@C60. The noble gas atoms, Ar, Kr, and Xe, are confined in the C60 to investigate the impact of charge migration from the entrapped atom to the C60 side. The present work concludes that the confinement oscillations in the photoionization features are amplified due to the charge migration. Further, the angle-resolved, spin average time delay is also investigated in the light of confinement. Features in the time delay due to the charge migration are more amplified relative to those in the cross-section or angular distribution.
Citation: Atoms
PubDate: 2022-04-30
DOI: 10.3390/atoms10020044
Issue No: Vol. 10, No. 2 (2022)
- Atoms, Vol. 10, Pages 45: Quasi-Static and Dynamic Photon Bubbles in Cold
Atom Clouds
Authors: João D. Rodrigues, Ruggero Giampaoli, José A. Rodrigues, António V. Ferreira, Hugo Terças, José T. Mendonça
First page: 45
Abstract: Turbulent radiation flow is ubiquitous in many physical systems where light–matter interaction becomes relevant. Photon bubble instabilities, in particular, have been identified as a possible source of turbulent radiation transport in astrophysical objects such as massive stars and black hole accretion disks. Here, we report on the experimental observation of a photon bubble instability in cold atomic gases, in the presence of multiple scattering of light. Two different regimes are identified, namely, the growth and formation of quasi-static structures of depleted atom density and increased photon number, akin to photon bubbles in astrophysical objects, and the destabilisation of these structures in a second regime of photon bubble turbulence. A two-fluid theory is developed to model the coupled atom–photon gas and to describe both the saturation of the instability in the regime of quasi-static bubbles and the low-frequency turbulent phase associated with the growth and collapse of photon bubbles inside the atomic sample. We also employ statistical dimensionality reduction techniques to describe the low-dimensional nature of the turbulent regime. The experimental results reported here, along with the theoretical model we have developed, may shed light on analogue photon bubble instabilities in astrophysical scenarios. Our findings are consistent with recent analyses based on spatially resolved pump–probe measurements.
Citation: Atoms
PubDate: 2022-04-30
DOI: 10.3390/atoms10020045
Issue No: Vol. 10, No. 2 (2022)
- Atoms, Vol. 10, Pages 46: Atomic Lifetime Data and Databases
Authors: Elmar Träbert
First page: 46
Abstract: Atomic-level lifetimes span a wide range, from attoseconds to years, relating to transition energy, multipole order, atomic core charge, relativistic effects, perturbation of atomic symmetries by external fields, and so on. Some parameters permit the application of simple scaling rules, others are sensitive to the environment. Which results deserve to be tabulated or stored in atomic databases' Which results require high accuracy to give insight into details of the atomic structure' Which data may be useful for the interpretation of plasma experiments or astrophysical observations without any particularly demanding accuracy threshold' Should computation on demand replace pre-fabricated atomic databases'
Citation: Atoms
PubDate: 2022-05-05
DOI: 10.3390/atoms10020046
Issue No: Vol. 10, No. 2 (2022)
- Atoms, Vol. 10, Pages 47: Superstructure and Distorted-Wave Codes and
Their Applications
Authors: Anand K. Bhatia
First page: 47
Abstract: There have been many observations of the solar and astrophysical spectra of various ions. The diagnostics of these observations require atomic data that include energy levels, oscillator strengths, transition rates, and collision strengths. These have been calculated using the Superstructure and Distorted-wave codes. We describe calculations for various ions. We calculate intensity ratios and compare them with observations to infer electron densities and temperatures of solar plasmas.
Citation: Atoms
PubDate: 2022-05-06
DOI: 10.3390/atoms10020047
Issue No: Vol. 10, No. 2 (2022)
- Atoms, Vol. 10, Pages 48: Electronic Structure of Lr+ (Z = 103) from Ab
Initio Calculations
Authors: Harry Ramanantoanina, Anastasia Borschevsky, Michael Block, Mustapha Laatiaoui
First page: 48
Abstract: The four-component relativistic Dirac–Coulomb Hamiltonian and the multireference configuration interaction (MRCI) model were used to provide the reliable energy levels and spectroscopic properties of the Lr+ ion and the Lu+ homolog. The energy spectrum of Lr+ is very similar to that of the Lu+ homolog, with the multiplet manifold of the 7s2, 6d17s1 and 7s17p1 configurations as the ground and low-lying excited states. The results are discussed in light of earlier findings utilizing different theoretical models. Overall, the MRCI model can reliably predict the energy levels and properties and bring new insight into experiments with superheavy ions.
Citation: Atoms
PubDate: 2022-05-09
DOI: 10.3390/atoms10020048
Issue No: Vol. 10, No. 2 (2022)
- Atoms, Vol. 10, Pages 49: No Cooperative Lamb Shift in Response of Thin
Slab to cw Beam of Resonant Light
Authors: Richard Friedberg, Jamal T. Manassah
First page: 49
Abstract: We review the definition of cooperative Lamb shift originally introduced by ourselves and S. R. Hartmann in 1973. We point out that the definition specified the preparation of a sample of identical two-level atoms prepared with partial excitation by a short pulse. We spell out in some detail the reasoning behind our assertion that the CLS does not enter into the dielectric constant, which determines the transmission of cw radiation through a sample. We give a prescription, using the transfer matrix formalism, for determining the transmission coefficient through a slab, given the thickness in wavelengths and the dielectric constant. We explore the possibility of achieving a true measurement of the CLS in a gaseous cold-atom cloud, with the help of a large foreign gas broadening of the resonant line.
Citation: Atoms
PubDate: 2022-05-09
DOI: 10.3390/atoms10020049
Issue No: Vol. 10, No. 2 (2022)
- Atoms, Vol. 10, Pages 50: TDCS Calculation for the Ionization of Nitrogen
Molecule by Electron Impact
Authors: Alpana Pandey, Ghanshyam Purohit
First page: 50
Abstract: Triple differential cross section (TDCS) results are reported for the electron impact ionization of nitrogen molecules. The TDCSs have been calculated in distorted wave Born formalism using orientation averaged molecular orbital (OAMO) approximation. The TDCS results are presented as average and weighted sum for the outer molecular orbital 3σg, 1πu, 2σu and the inner 2σg molecular orbital. The obtained theoretical TDCSs are compared with the available measurements. The results are analysed in terms of the positions and relative intensities of binary and recoil peaks. Within a first order model and for a complex molecule, a reasonable agreement is obtained with the experimental data in the binary peak region with certain discrepancies in position and magnitude in the recoil peak region.
Citation: Atoms
PubDate: 2022-05-18
DOI: 10.3390/atoms10020050
Issue No: Vol. 10, No. 2 (2022)
- Atoms, Vol. 10, Pages 6: Long-Range Interactions for Hydrogen Atoms in
Excited D States
Authors: Chandra M. Adhikari, Ulrich D. Jentschura
First page: 6
Abstract: Pressure shifts inside an atomic beam are among the more theoretically challenging effects in high-precision measurements of atomic transitions. A crucial element in their theoretical analysis is the understanding of long-range interatomic interactions inside the beam. For excited reference states, the presence of quasi-degenerate states leads to additional challenges, due to the necessity to diagonalize large matrices in the quasi-degenerate hyperfine manifolds. Here, we focus on the interactions of hydrogen atoms in reference states composed of an excited nD state (atom A), and in the metastable 2S state (atom B). We devote special attention to the cases n=3 and n=8. For n=3, the main effect is generated by quasi-degenerate virtual P states from both atoms A and B and leads to experimentally relevant second-order long-range (van-der-Waals) interactions proportional to the sixth inverse power of the interatomic distance. For n=8, in addition to virtual states with two states of P symmetry, one needs to take into account combined virtual P and F states from atoms A and B. The numerical value of the so-called C6 coefficients multiplying the interaction energy was found to grow with the principal quantum number of the reference D state; it was found to be of the order of 1011 in atomic units. The result allows for the calculation of the pressure shift inside atomic beams while driving transitions to nD states.
Citation: Atoms
PubDate: 2022-01-05
DOI: 10.3390/atoms10010006
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 7: Level Structure and Properties of Open f-Shell
Elements
Authors: Stephan Fritzsche
First page: 7
Abstract: Open f-shell elements still constitute a great challenge for atomic theory owing to their (very) rich fine-structure and strong correlations among the valence-shell electrons. For these medium and heavy elements, many atomic properties are sensitive to the correlated motion of electrons and, hence, require large-scale computations in order to deal consistently with all relativistic, correlation and rearrangement contributions to the electron density. Often, different concepts and notations need to be combined for just classifying the low-lying level structure of these elements. With Jac, the Jena Atomic Calculator, we here provide a toolbox that helps to explore and deal with such elements with open d- and f-shell structures. Based on Dirac’s equation, Jac is suitable for almost all atoms and ions across the periodic table. As an example, we demonstrate how reasonably accurate computations can be performed for the low-lying level structure, transition probabilities and lifetimes for Th2+ ions with a 5f6d ground configuration. Other, and more complex, shell structures are supported as well, though often for a trade-off between the size and accuracy of the computations. Owing to its simple use, however, Jac supports both quick estimates and detailed case studies on open d- or f-shell elements.
Citation: Atoms
PubDate: 2022-01-12
DOI: 10.3390/atoms10010007
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 8: Elastic and Inelastic Cross Sections for
Low-Energy Electron Collisions with ClF Molecule Using the R-Matrix Method
Authors: Monika Bassi, Anand Bharadvaja, Kasturi Lal Baluja
First page: 8
Abstract: The ClF molecule belongs to an interhalogen family and is important in laser physics and condensed phase molecular dynamics. The elastic and excitation scattering cross sections are obtained in a fixed nuclei approximation using the UKRmol+ codes based on R-matrix formalism. The scattering calculations were performed in the static-exchange (SE), static-exchange-plus-polarisation (SEP), and close-coupling (CC) models. Three CC models with different target states were employed, namely, the 1-state, 5-states, and 12-states. In the CC model, the target states were represented by configuration interaction (CI) wavefunctions. A good agreement of dipole and quadrupole moments of the ground state was obtained with the experimental values, which indicates a good representation of the target modelling. The study predicted the existence of a shape resonance in the SE, SEP, and 5-states CC models. This resonance vanished in the 12-states CC model. The excitation cross sections from ground to the lowest two excited states were also reported. The elastic differential and momentum transfer cross sections were obtained in the 12-states CC models. The contribution of long-range interactions to elastic scattering was included via Born closure approach. The quantities like collision frequencies and rate coefficients were also presented over a wide range of electron temperatures. The ionization cross sections were computed using the binary-encounter-Bethe (BEB) model. The results were reported in C2v point group representation.
Citation: Atoms
PubDate: 2022-01-19
DOI: 10.3390/atoms10010008
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 9: Photoejection from Various Systems and
Radiative-Rate Coefficients
Authors: Anand K. Bhatia
First page: 9
Abstract: Photoionization or photodetachment is an important process. It has applications in solar- and astrophysics. In addition to accurate wave function of the target, accurate continuum functions are required. There are various approaches, like exchange approximation, method of polarized orbitals, close-coupling approximation, R-matrix formulation, exterior complex scaling, the recent hybrid theory, etc., to calculate scattering functions. We describe some of them used in calculations of photodetachment or photoabsorption cross sections of ions and atoms. Comparisons of cross sections obtained using different approaches for the ejected electron are given. Furthermore, recombination rate coefficients also are also important in solar- and astrophysics and they have been calculated at various electron temperatures using the Maxwell velocity distribution function. Approaches based on the method of polarized orbitals do not provide any resonance structure of photoabsorption cross sections, in spite of the fact that accurate results have been obtained away from the resonance region and in the resonance region by calculating continuum functions to calculate resonance widths using phase shifts in the Breit–Wigner formula for calculating resonance parameters. Accurate resonance parameters in the elastic cross sections have been obtained using the hybrid theory and they compare well with those obtained using the Feshbach formulation. We conclude that accurate results for photoabsorption cross sections can be obtained using the hybrid theory.
Citation: Atoms
PubDate: 2022-01-19
DOI: 10.3390/atoms10010009
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 10: Exploring the Excited-State Nonadiabatic Effects
in the Semisaturated Planar Tetracoordinated Carbon Molecule C7H4
Authors: Chithra Jayakumari, Probal Nag, Sai Isukapalli, Sivaranjana Vennapusa
First page: 10
Abstract: We theoretically study the nonadiabatic relaxation dynamics of low-lying singlet excited-states of semisaturated planar tetracoordinated carbon molecule, C7H4. This molecule possesses a stable C2v ground-state equilibrium geometry. The three low-lying singlet states, S1, S2 and S3, lie in the energy gap of about 1.2 eV. The potential energy surfaces constructed within the quadratic vibronic coupling formalism reveal multiple conical intersections in the Franck-Condon region. Upon photoexcitation to S3, the wavepacket decays rapidly to lower states via these conical intersections. We also observe the wavepacket transfer to S3 during the initial wavepacket evolution on lower states, suggesting the nonadiabatic behavior of photoexcited planar C7H4.
Citation: Atoms
PubDate: 2022-01-19
DOI: 10.3390/atoms10010010
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 11: Two-Center Basis Generator Method Calculations
for Li3+, C3+ and O3+ Ion Impact on Ground State Hydrogen
Authors: Anthony C. K. Leung, Tom Kirchner
First page: 11
Abstract: The two-center basis generator method is used to obtain cross sections for excitation, capture, and ionization in Li3+, C3+, and O3+ collisions with ground-state hydrogen at projectile energies from 1 to 100 keV/u. The interaction of the C3+ and O3+ projectiles with the active electron is represented by a model potential. Comparisons of cross sections with previously reported data show an overall good agreement, while discrepancies in capture for C3+ collisions at low energies are noted. The present results show that excitation and ionization are similar across the three collision systems, which indicates that these cross sections are mostly dependent on the net charge of the projectile only. The situation is different for the capture channel.
Citation: Atoms
PubDate: 2022-01-21
DOI: 10.3390/atoms10010011
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 12: Two-Dimensional Six-Body van der Waals
Interactions
Authors: Jianing Han
First page: 12
Abstract: Van der Waals interactions, primarily attractive van der Waals interactions, have been studied over one and half centuries. However, repulsive van der Waals interactions are less widely studied than attractive van der Waals interactions. In this article, we focus on repulsive van der Waals interactions. Van der Waals interactions are dipole–dipole interactions. In this article, we study the van der Waals interactions between multiple dipoles. Specifically, we focus on two-dimensional six-body van der Waals interactions. This study has many potential applications. For example, the result may be applied to physics, chemistry, chemical engineering, and other fields of sciences and engineering, such as breaking molecules.
Citation: Atoms
PubDate: 2022-01-24
DOI: 10.3390/atoms10010012
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 13: Single Ionization of He by Energetic Protons in
a Parabolic Quasi-Sturmians Approach
Authors: Sergey A. Zaytsev, Alexander S. Zaytsev, Vyacheslav V. Nasyrov, Darya S. Zaytseva, Lorenzo U. Ancarani, Konstantin A. Kouzakov
First page: 13
Abstract: A fully differential cross section for single ionization of helium induced by 1 MeV proton impact is calculated using the parabolic convoluted quasi-Sturmian (CQS) method. In the framework of this approach the transition amplitude is extracted directly from the asymptotic behavior of the solution of an inhomogeneous Schrödinger equation for the Coulomb three-body system (e−,He+,p+). The driven equation is solved numerically by expanding in convolutions of quasi-Sturmians for the two-body proton-He+ and electron-He+ systems. It is found, at least in the high energy limit, that the calculated cross sections within the proposed CQS method converge quickly as the number of terms in the expansions is increased, and are in reasonable agreement with experimental data and other theoretical results.
Citation: Atoms
PubDate: 2022-01-25
DOI: 10.3390/atoms10010013
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 14: Cartesian Operator Factorization Method for
Hydrogen
Authors: Xinliang Lyu, Christina Daniel, James K. Freericks
First page: 14
Abstract: We generalize Schrödinger’s factorization method for Hydrogen from the conventional separation into angular and radial coordinates to a Cartesian-based factorization. Unique to this approach is the fact that the Hamiltonian is represented as a sum over factorizations in terms of coupled operators that depend on the coordinates and momenta in each Cartesian direction. We determine the eigenstates and energies, the wavefunctions in both coordinate and momentum space, and we also illustrate how this technique can be employed to develop the conventional confluent hypergeometric equation approach. The methodology developed here could potentially be employed for other Hamiltonians that can be represented as the sum over coupled Schrödinger factorizations.
Citation: Atoms
PubDate: 2022-01-26
DOI: 10.3390/atoms10010014
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 15: Acknowledgment to Reviewers of Atoms in 2021
Authors: Atoms Editorial Office Atoms Editorial Office
First page: 15
Abstract: Rigorous peer-reviews are the basis of high-quality academic publishing [...]
Citation: Atoms
PubDate: 2022-01-27
DOI: 10.3390/atoms10010015
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 16: Atomic Processes, Including Photoabsorption,
Subject to Outside Charge-Neutral Plasma
Authors: Tu-Nan Chang, Te-Kuei Fang, Chensheng Wu, Xiang Gao
First page: 16
Abstract: We present in this review our recent theoretical studies on atomic processes subject to the plasma environment including the α and β emissions and the ground state photoabsorption of the one- and two-electron atoms and ions. By carefully examining the spatial and temporal criteria of the Debye–Hückel (DH) approximation based on the classical Maxwell–Boltzmann statistics, we were able to represent the plasma effect with a Debye–Hückel screening potential VDH in terms of the Debye length D, which is linked to the ratio between the plasma density N and its temperature kT. Our theoretical data generated with VDH from the detailed non-relativistic and relativistic multiconfiguration atomic structure calculations compare well with the limited measured results from the most recent experiments. Starting from the quasi-hydrogenic picture, we were able to show qualitatively that the energy shifts of the emission lines could be expressed in terms of a general expression as a function of a modified parameter, i.e., the reduced Debye length λ. The close agreement between theory and experiment from our study may help to facilitate the plasma diagnostics to determine the electron density and the temperature of the outside plasma.
Citation: Atoms
PubDate: 2022-01-29
DOI: 10.3390/atoms10010016
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 17: Electron Impact Excitation of Ge-like
Te20+–Cd16+ Ions
Authors: Pooja Malker, Lalita Sharma
First page: 17
Abstract: We study electron impact excitation of dipole allowed transitions in the extreme ultraviolet range—8–55 nm—for the germanium isoelectronic sequence Te20+–Cd16+. The fine structure transitions between the ground state having configuration 4s24p2 and the excited states with configurations 4s4p3 and 4s24p4d are considered for these ions. We employ the relativistic distorted wave method to calculate the excitation cross sections in the incident electron energy range from the excitation threshold to 5000 eV. To obtain the required ionic bound state wavefunctions we have used the multi-configuration Dirac-Fock method with correlations within the n = 5 complexes as well as performed relativistic configuration interaction calculations to include the quantum electrodynamic effects. The accuracy of these wavefunctions is established by comparing our calculated wavelengths and oscillator strengths of the considered transitions with the previously reported measurements and other available theoretical results. We also provide the fitting parameters of the calculated cross sections and the excitation rate coefficients for their direct applications in plasma modeling.
Citation: Atoms
PubDate: 2022-02-07
DOI: 10.3390/atoms10010017
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 18: Structure Calculations in Nd III and U III
Relevant for Kilonovae Modelling
Authors: Ricardo F. Silva, Jorge M. Sampaio, Pedro Amaro, Andreas Flörs, Gabriel Martínez-Pinedo, José P. Marques
First page: 18
Abstract: The detection of gravitational waves and electromagnetic signals from the neutron star merger GW170817 has provided evidence that these astrophysical events are sites where the r-process nucleosynthesis operates. The electromagnetic signal, commonly known as kilonova, is powered by the radioactive decay of freshly synthesized nuclei. However, its luminosity, colour and spectra depend on the atomic opacities of the produced elements. In particular, opacities of lanthanides and actinides elements, due to their large density of bound–bound transitions, are fundamental. The current work focuses on atomic structure calculations for lanthanide and actinide ions, which are important in kilonovae modelling of ejecta spectra. Calculations for Nd III and U III, two representative rare-earth ions, were achieved. Our aim is to provide valuable insights for future opacity calculations for all heavy elements. We noticed that the opacity of U III is about an order of magnitude greater than the opacity of Nd III due to a higher density of levels in the case of the actinide.
Citation: Atoms
PubDate: 2022-02-07
DOI: 10.3390/atoms10010018
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 19: Static Impurities in a Weakly Interacting Bose
Gas
Authors: Galyna Panochko, Volodymyr Pastukhov
First page: 19
Abstract: We present a comprehensive discussion of the ground-state properties of dilute D-dimensional Bose gas interacting with a few static impurities. Assuming the short-ranged character of the boson-impurity interaction, we calculated the energy of three- and two-dimensional Bose systems with one and two impurities immersed.
Citation: Atoms
PubDate: 2022-02-08
DOI: 10.3390/atoms10010019
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 20: Quantum Dynamics of Hydrogen-like Ions in a
Spatially Nonuniform Magnetic Field: A Possible Application to Fusion
Plasma
Authors: Sara Fadhel, Mohammed Tayeb Meftah, Keltoum Chenini
First page: 20
Abstract: In this work, we direct our attention to the study of the effect of a nonuniform and strong magnetic field on the quantum properties of ions in plasma. We have assumed that the strong magnetic field is a sum of two magnetic fields: one, the most intense, has a toroidal geometry, whereas the other of less intensity (about the third of the first) is poloidal. Regarding the quantum properties, we have focused our attention on obtaining the corresponding eigenenergy of n hydrogen-like ion in this nonuniform magnetic field. Using the obtained eigenenergy, we investigated the spectral line shape (Lyman-alpha) of three types of ions: He+, C5+, and Ar17+ for different magnetic field magnitudes. In this study, we considered only Doppler and electronic Stark broadening of the spectral line shapes.
Citation: Atoms
PubDate: 2022-02-08
DOI: 10.3390/atoms10010020
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 21: First Offline Results from the S3 Low-Energy
Branch
Authors: Jekabs Romans, Anjali Ajayakumar, Martial Authier, Frederic Boumard, Lucia Caceres, Jean-François Cam, Arno Claessens, Samuel Damoy, Pierre Delahaye, Philippe Desrues, Antoine Drouart, Patricia Duchesne, Rafael Ferrer, Xavier Fléchard, Serge Franchoo, Patrice Gangnant, Ruben P. de Groote, Sandro Kraemer, Nathalie Lecesne, Renan Leroy, Julien Lory, Franck Lutton, Vladimir Manea, Yvan Merrer, Iain Moore, Alejandro Ortiz-Cortes, Benoit Osmond, Julien Piot, Olivier Pochon, Blaise-Maël Retailleau, Hervé Savajols, Simon Sels, Emil Traykov, Juha Uusitalo, Christophe Vandamme, Marine Vandebrouck, Paul Van den Bergh, Piet Van Duppen, Matthias Verlinde, Elise Verstraelen, Klaus Wendt
First page: 21
Abstract: We present the first results obtained from the S3 Low-Energy Branch , the gas cell setup at SPIRAL2-GANIL, which will be installed behind the S3 spectrometer for atomic and nuclear spectroscopy studies of exotic nuclei. The installation is currently being commissioned offline, with the aim to establish optimum conditions for the operation of the radio frequency quadrupole ion guides, mass separation and ion bunching, providing high-efficiency and low-energy spatial spread for the isotopes of interest. Transmission and mass-resolving power measurements are presented for the different components of the S3-LEB setup. In addition, a single-longitudinal-mode, injection-locked, pumped pulsed-titanium–sapphire laser system has been recently implemented and is used for the first proof-of-principle measurements in an offline laser laboratory. Laser spectroscopy measurements of erbium, which is the commissioning case of the S3 spectrometer, are presented using the 4f126s23H6→4f12(3H)6s6p optical transition.
Citation: Atoms
PubDate: 2022-02-09
DOI: 10.3390/atoms10010021
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 22: Taking the Convergent Close-Coupling Method
beyond Helium: The Utility of the Hartree-Fock Theory
Authors: Igor Bray, Xavier Weber, Dmitry V. Fursa, Alisher S. Kadyrov, Barry I. Schneider, Sudhakar Pamidighantam, Maciej Cytowski, Anatoli S. Kheifets
First page: 22
Abstract: The convergent close-coupling (CCC) method was initially developed to describe electron scattering on atomic hydrogen and the hydrogenic ions such as He+. The latter allows implementation of double photoionization (DPI) of the helium atom. For more complex single valence-electron atomic and ionic targets, the direct and exchange interaction with the inner electron core needs to be taken into account. For this purpose, the Hartree-Fock (HF) computer codes developed in the group of Miron Amusia have been adapted. In this brief review article, we demonstrate the utility of the HF technique by examples of electron scattering on Li and the DPI of the H− and Li− ions. We also discuss that modern-day computer infrastructure allows the associated CCC code, and others, to be readily run directly via the Atomic, Molecular and Optical Science Gateway.
Citation: Atoms
PubDate: 2022-02-11
DOI: 10.3390/atoms10010022
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 23: Double Photoionization of Atomic Carbon
Authors: Frank L. Yip
First page: 23
Abstract: Double photoionization events provide a direct evaluation of electron correlation. The recent focus on few-electron targets continues to reveal the consequences of electron correlation for targets that possess several electrons. We consider the double photoionization of the 2p2 valence electrons of atomic carbon and focus on the first energetically accessible final-state symmetries that originate from coupling the active electrons in 3P configurations, which are doubly ionized by a single photon. Comparison of this process in carbon with neon provides an analogous case for the resulting final-state symmetries within the framework where the ejected electrons are influenced by the remaining bound electrons in a frozen-core approximation. Choosing this symmetry allows for comparison with previous theoretical results for total and energy sharing cross-sections of carbon. Fully differential cross-sections for both carbon and neon are also compared.
Citation: Atoms
PubDate: 2022-02-12
DOI: 10.3390/atoms10010023
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 24: Extending Our Knowledge about the 229Th Nuclear
Isomer
Authors: Benedict Seiferle, Daniel Moritz, Kevin Scharl, Shiqian Ding, Florian Zacherl, Lilli Löbell, Peter G. Thirolf
First page: 24
Abstract: The first nuclear excited state in 229Th possesses the lowest excitation energy of all currently known nuclear levels. The energy difference between the ground- and first-excited (isomeric) state (denoted with 229mTh) amounts only to ≈8.2 eV (≈151.2 nm), which results in several interesting consequences: Since the excitation energy is in the same energy range as the binding energy of valence electrons, the lifetime of 229mTh is strongly influenced by the electronic structure of the Th atom or ion. Furthermore, it is possible to potentially excite the isomeric state in 229Th with laser radiation, which led to the proposal of a nuclear clock that could be used to search for new physics beyond the standard model. In this article, we will focus on recent technical developments in our group that will help to better understand the decay mechanisms of 229mTh, focusing primarily on measuring the radiative lifetime of the isomeric state.
Citation: Atoms
PubDate: 2022-02-14
DOI: 10.3390/atoms10010024
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 25: Mechanisms of Electron-Induced Chemistry in
Molecular Ices
Authors: Fabian Schmidt, Tobias Borrmann, Martin Philipp Mues, Sanna Benter, Petra Swiderek, Jan Hendrik Bredehöft
First page: 25
Abstract: Electron-induced chemistry is relevant to many processes that occur when ionizing radiation interacts with matter. This includes radiation damage, curing of polymers, and nanofabrication processes but also the formation of complex molecules in molecular ices grown on dust particles in space. High-energy radiation liberates from such materials an abundance of secondary electrons of which most have energies below 20 eV. These electrons efficiently trigger reactions when they attach to molecules or induce electronic excitation and further ionization. This review focuses on the present state of insight regarding the mechanisms of reactions induced by electrons with energies between 0 and 20 eV that lead to formation of larger products in binary ice layers consisting of small molecules (H2O, CO, CH3OH, NH3, CH4, C2H4, CH3CN, C2H6) or some derivatives thereof (C2H5NH2 and (C2H5)2NH, CH2=CHCH3). It summarizes our approach to identify products and quantify their amounts based on thermal desorption spectrometry (TDS) and electron-stimulated desorption (ESD) experiments performed in ultrahigh vacuum (UHV). The overview of the results demonstrates that, although the initial electron-molecule interaction is a non-thermal process, product formation from the resulting reactive species is often governed by subsequent reactions that follow well-known thermal and radical-driven mechanisms of organic chemistry.
Citation: Atoms
PubDate: 2022-02-21
DOI: 10.3390/atoms10010025
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 26: Generalizations of the R-Matrix Method to the
Treatment of the Interaction of Short-Pulse Electromagnetic Radiation with
Atoms
Authors: Barry I. Schneider, Kathryn R. Hamilton, Klaus Bartschat
First page: 26
Abstract: Since its initial development in the 1970s by Phil Burke and his collaborators, the R-matrix theory and associated computer codes have become the method of choice for the calculation of accurate data for general electron–atom/ion/molecule collision and photoionization processes. The use of a non-orthogonal set of orbitals based on B-splines, now called the B-spline R-matrix (BSR) approach, was pioneered by Zatsarinny. It has considerably extended the flexibility of the approach and improved particularly the treatment of complex many-electron atomic and ionic targets, for which accurate data are needed in many modelling applications for processes involving low-temperature plasmas. Both the original R-matrix approach and the BSR method have been extended to the interaction of short, intense electromagnetic (EM) radiation with atoms and molecules. Here, we provide an overview of the theoretical tools that were required to facilitate the extension of the theory to the time domain. As an example of a practical application, we show results for two-photon ionization of argon by intense short-pulse extreme ultraviolet radiation.
Citation: Atoms
PubDate: 2022-02-22
DOI: 10.3390/atoms10010026
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 27: Persistent Planar Tetracoordinate Carbon in
Global Minima Structures of Silicon-Carbon Clusters
Authors: Luis Leyva-Parra, Diego Inostroza, Osvaldo Yañez, Julio César Cruz, Jorge Garza, Víctor García, William Tiznado
First page: 27
Abstract: Recently, we reported a series of global minima whose structures consist of carbon rings decorated with heavier group 14 elements. Interestingly, these structures feature planar tetracoordinate carbons (ptCs) and result from the replacement of five or six protons (H+) from the cyclopentadienyl anion (C5H5−) or the pentalene dianion (C8H62−) by three or four E2+ dications (E = Si–Pb), respectively. The silicon derivatives of these series are the Si3C5 and Si4C8 clusters. Here we show that ptC persists in some clusters with an equivalent number of C and Si atoms, i.e., Si5C5, Si8C8, and Si9C9. In all these species, the ptC is embedded in a pentagonal C5 ring and participates in a three-center, two-electron (3c-2e) Si-ptC-Si σ-bond. Furthermore, these clusters are π-aromatic species according to chemical bonding analysis and magnetic criteria.
Citation: Atoms
PubDate: 2022-02-28
DOI: 10.3390/atoms10010027
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 28: Bernstein–Greene–Kruskal and
Case–Van Kampen Modes for the Landau–Vlasov Equation
Authors: Fernando Haas, Rodrigo Vidmar
First page: 28
Abstract: The one-dimensional Landau–Vlasov equation describing ultracold dilute bosonic gases in the mean-field collisionless regime under strong transverse confinement is analyzed using traditional methods of plasma physics. Time-independent, stationary solutions are found using a similar approach as for the Bernstein–Greene–Kruskal nonlinear plasma modes. Linear stationary waves similar to the Case–Van Kampen plasma normal modes are also shown to be available. The new bosonic solutions have no decaying or growth properties, in the same sense as the analog plasma solutions. The results are applied for real ultracold bosonic gases accessible in contemporary laboratory experiments.
Citation: Atoms
PubDate: 2022-03-01
DOI: 10.3390/atoms10010028
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 29: Ultra-Dilute Gas of Polarons in a
Bose–Einstein Condensate
Authors: Luis A. Peña Ardila
First page: 29
Abstract: We investigate the properties of a dilute gas of impurities embedded in an ultracold gas of bosons that forms a Bose–Einstein condensate (BEC). This work focuses mainly on the equation of state (EoS) of the impurity gas at zero temperature and the induced interaction between impurities mediated by the host bath. We use perturbative field-theory approaches, such as Hugenholtz–Pines formalism, in the weakly interacting regime. In turn, for strong interactions, we aim at non-perturbative techniques such as quantum–Monte Carlo (QMC) methods. Our findings agree with experimental observations for an ultra dilute gas of impurities, modeled in the framework of the single impurity problem; however, as the density of impurities increases, systematic deviations are displayed with respect to the one-body Bose polaron problem.
Citation: Atoms
PubDate: 2022-03-02
DOI: 10.3390/atoms10010029
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 30: Applications of Cold-Atom-Based Quantum
Technology
Authors: Jamie Vovrosh, Yu-Hung Lien
First page: 30
Abstract: Cold-atom systems are rapidly advancing in technical maturity and have, in many cases, surpassed their classical counterparts, becoming a versatile tool that is used in a variety of fundamental research applications [...]
Citation: Atoms
PubDate: 2022-03-09
DOI: 10.3390/atoms10010030
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 31: A Theoretical Study of Scattering of Electrons
and Positrons by CO2 Molecule
Authors: M. Masum Billah, M. Mousumi Khatun, M. M. Haque, M. Yousuf Ali, Mahmudul H. Khandker, A. K. F. Haque, Hiroshi Watabe, M. Alfaz Uddin
First page: 31
Abstract: This article presents a theoretical investigation of the differential, integrated, elastic, inelastic, total, momentum-transfer, and viscosity cross-sections, along with the total ionization cross-section, for elastically scattered electrons and positrons from a carbon dioxide (CO2) molecule in the incident energy range of 1 eV ≤Ei≤ 1 MeV. In addition, for the first time, we report the spin polarization of e±−CO2 scattering systems. The independent atom model (IAM) with screening correction (IAMS) using a complex optical potential was employed to solve the Dirac relativistic equation in partial-wave analysis. The comparison of our results with the available experimental data and other theoretical predictions shows a reasonable agreement in the intermediate- and high-energy regions.
Citation: Atoms
PubDate: 2022-03-09
DOI: 10.3390/atoms10010031
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 32: Demonstration of a Compact Magneto-Optical Trap
on an Unstaffed Aerial Vehicle
Authors: Luuk Earl, Jamie Vovrosh, Michael Wright, Daniel Roberts, Jonathan Winch, Marisa Perea-Ortiz, Andrew Lamb, Farzad Hayati, Paul Griffin, Nicole Metje, Kai Bongs, Michael Holynski
First page: 32
Abstract: The extraordinary performance offered by cold atom-based clocks and sensors has the opportunity to profoundly affect a range of applications, for example in gravity surveys, enabling long term monitoring applications through low drift measurements. While ground-based devices are already starting to enter the commercial market, significant improvements in robustness and reductions to size, weight, and power are required for such devices to be deployed by Unstaffed Aerial Vehicle systems (UAV). In this article, we realise the first step towards the deployment of cold atom based clocks and sensors on UAV’s by demonstrating an UAV portable magneto-optical trap system, the core package of cold atom based systems. This system is able to generate clouds of 2.1±0.2×107 atoms, in a package of 370 mm × 350 mm × 100 mm, weighing 6.56 kg, consuming 80 W of power.
Citation: Atoms
PubDate: 2022-03-17
DOI: 10.3390/atoms10010032
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 33: Inelastic Processes in Strontium-Hydrogen
Collisions and Their Impact on Non-LTE Calculations
Authors: Svetlana A. Yakovleva, Andrey K. Belyaev, Lyudmila I. Mashonkina
First page: 33
Abstract: Inelastic processes rate coefficients for low-energy Sr + H, Sr+ + H−, Sr+ + H, and Sr2+ + H− collisions are calculated using the multichannel quantum model approach. A total of 31 scattering channels of SrH+ and 17 scattering channels of SrH are considered. The partial cross sections and the partial rate coefficients are hence calculated for 1202 partial processes in total. Using new quantum data for Sr ii + H i collisions, we updated the model atom of Sr ii and performed the non-local thermodynamic equilibrium (non-LTE) calculations. We provide the non-LTE abundance corrections for the Sr ii resonance lines in two grids of model atmospheres, which are applicable to very metal-poor ([Fe/H] ≤−2) dwarfs and giants.
Citation: Atoms
PubDate: 2022-03-17
DOI: 10.3390/atoms10010033
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 10, Pages 34: Modeling Atom Interferometry Experiments with
Bose–Einstein Condensates in Power-Law Potentials
Authors: Stephen Thomas, Colson Sapp, Charles Henry, Andrew Smith, Charles A. Sackett, Charles W. Clark, Mark Edwards
First page: 34
Abstract: Recent atom interferometry (AI) experiments involving Bose–Einstein condensates (BECs) have been conducted under extreme conditions of volume and interrogation time. Numerical solution of the rotating-frame Gross–Pitaevskii equation (RFGPE), which is the standard mean-field theory applied to these experiments, is impractical due to the excessive computation time and memory required. We present a variational model that provides approximate solutions of the RFGPE for a power-law potential on a practical time scale. This model is well-suited to the design and analysis of AI experiments involving BECs that are split and later recombined to form an interference pattern. We derive the equations of motion of the variational parameters for this model and illustrate how the model can be applied to the sequence of steps in a recent AI experiment where BECs were used to implement a dual-Sagnac atom interferometer rotation sensor. We use this model to investigate the impact of finite-size and interaction effects on the single-Sagnac-interferometer phase shift.
Citation: Atoms
PubDate: 2022-03-21
DOI: 10.3390/atoms10010034
Issue No: Vol. 10, No. 1 (2022)
- Atoms, Vol. 9, Pages 70: Quantum Confinement Effects of Thin Co3O4 Films
Authors: Alexandros Barnasas, Christos S. Garoufalis, Dimitrios I. Anyfantis, Nikolaos Bouropoulos, Panagiotis Poulopoulos, David B. Hayrapetyan, Sotirios Baskoutas
First page: 70
Abstract: Thin Co films were deposited on quartz and Corning glass by radio frequency magnetron sputtering. The films were postannealed at 500 °C in a furnace in air atmosphere. The resulting samples were examined with X-ray diffraction experiments, which revealed that they consist of single-phase, polycrystalline Co3O4. The morphology of selected samples was recorded by atomic force microscopy. Ultraviolet-visible light absorption spectroscopy experiments probed the absorbance of the films in the wavelength range 200–1,100 nm. Two types of transitions (energy gaps) were clearly identified. Both of them were found to be “blue shifted” with decreasing film thickness; this is interpreted as evidence of quantum confinement effects. For the case of the first gap value, this was corroborated by calculations based on a combination of the Potential Morphing Method and the effective mass approximation.
Citation: Atoms
PubDate: 2021-09-22
DOI: 10.3390/atoms9040070
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 71: Magnetic Angle Changer for Studies of
Electronically Excited Long-Living Atomic States
Authors: Łukasz Kłosowski, Mariusz Piwiński
First page: 71
Abstract: A new geometry of a magnetic angle changer (MAC) device is proposed, which allows experiments to be run on electron impact excitation of long-lived states of target atoms. The details of the device’s design are presented and discussed together with a numerical analysis of its magnetic field.
Citation: Atoms
PubDate: 2021-09-28
DOI: 10.3390/atoms9040071
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 72: Calculation of the Lowest Resonant States of H−
and Li by the Complex Absorbing Potential Method
Authors: Sergey O. Adamson, Daria D. Kharlampidi, Yurii A. Dyakov, Gennady V. Golubkov, Maxim G. Golubkov
First page: 72
Abstract: The analysis of the features of the method of complex absorbing potential (CAP) is carried out for a single-channel problem with an explicit parameterization of the scattering matrix. It is shown that there can be several types of CAP trajectories depending on the choice of the initial conditions. In any case, the estimation of the resonance parameters from the position of the optimal trajectory point can lead to a systematic error or an ambiguous result. In special cases, the search for the optimal point can be replaced by the averaging over a closed section of the trajectory. The CAP trajectories constructed in the H− and Li resonance calculations correlate well with the model trajectories, which have a curl around the resonance. The averaging over a closed area of the trajectory leads to better estimates of the energy and width of the resonance in comparison with the technique of searching for the optimal point.
Citation: Atoms
PubDate: 2021-09-30
DOI: 10.3390/atoms9040072
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 73: Photoionization and Electron-Ion Recombination of
n = 1 to Very High n-Values of Hydrogenic Ions
Authors: Sultana N. Nahar
First page: 73
Abstract: Single electron hydrogen or hydrogenic ions have analytical forms to evaluate the atomic parameters for the inverse processes of photoionization and electron-ion recombination (H I + hν↔ H II + e) where H is hydrogen. Studies of these processes have continued until the present day (i) as the computations are restricted to lower principle quantum number n and (ii) to improve the accuracy. The analytical expressions have many terms and there are numerical instabilities arising from cancellations of terms. Strategies for fast convergence of contributions were developed but precise computations are still limited to lower n. This report gives a brief review of the earlier precise methodologies for hydrogen, and presents numerical tables of photoionization cross sections (σPI), and electron-ion recombination rate coefficients (αRC) obtained from recombination cross sections (σRC) for all n values going to a very high value of 800. σPI was obtained using the precise formalism of Burgess and Seaton, and Burgess. αRC was obtained through a finite integration that converge recombination exactly as implemented in the unified method of recombination of Nahar and Pradhan. Since the total electron-ion recombination includes all levels for n = 1 −∞, the total asymptotic contribution of n=801−∞, called the top-up, is obtained through a n−3 formula. A FORTRAN program “hpxrrc.f” is provided to compute photoionization cross sections, recombination cross sections and rate coefficients for any nl. The results on hydrogen atom can be used to obtain those for any hydrogenic ion of charge z through z-scaling relations provided in the theory section. The present results are of high precision and complete for astrophysical modelings.
Citation: Atoms
PubDate: 2021-10-03
DOI: 10.3390/atoms9040073
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 74: Electron Ionization of Size-Selected Positively
and Negatively Charged Helium Droplets
Authors: Felix Laimer, Fabio Zappa, Elisabeth Gruber, Paul Scheier
First page: 74
Abstract: A beam of size-selected charged helium droplets was crossed with an electron beam, and the ion efficiency curves for the product droplets in all different charge states were recorded. We estimate that the selected helium droplets on their passage through the electron beam are hit by several hundred electrons which can interact with the individual He atoms of the droplets. Reaction channels corresponding to the removal or capture of up to eight electrons were identified, and in all cases, inelastic scattering and the formation of metastable helium played a significant role.
Citation: Atoms
PubDate: 2021-10-05
DOI: 10.3390/atoms9040074
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 75: Linear and Nonlinear Optical Absorption of
CdSe/CdS Core/Shell Quantum Dots in the Presence of Donor Impurity
Authors: Grigor A. Mantashian, Nare A. Zaqaryan, Paytsar A. Mantashyan, Hayk A. Sarkisyan, Sotirios Baskoutas, David B. Hayrapetyan
First page: 75
Abstract: Linear and nonlinear optical properties in colloidal CdSe/CdS core/shell quantum dots with different sizes have been theoretically investigated in the framework of effective mass approximation. The electron states in colloidal CdSe/CdS core/shell quantum dots have been calculated using the finite element method. The intraband linear and nonlinear absorption spectra have been calculated for colloidal CdSe/CdS core/shell quantum dots with different sizes. In addition, the dependences of the linear and nonlinear refractive index change on the incident light energy have been calculated. In the last section of the paper the second- and third-order harmonic generation spectra have been presented.
Citation: Atoms
PubDate: 2021-10-05
DOI: 10.3390/atoms9040075
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 76: Electron Impact Excitation of Extreme
Ultra-Violet Transitions in Xe7+ – Xe10+ Ions
Authors: Aloka Kumar Sahoo, Lalita Sharma
First page: 76
Abstract: In the present work, a detailed study on the electron impact excitation of Xe7+, Xe8+, Xe9+ and Xe10+ ions for the dipole allowed (E1) transitions in the EUV range of 8–19 nm is presented. The multi-configuration Dirac–Fock method is used for the atomic structure calculation including the Breit and QED corrections along with the relativistic configuration interaction approach. We have compared our calculated energy levels, wavelengths and transition rates with other reported experimental and theoretical results. Further, the relativistic distorted wave method is used to calculate the cross sections from the excitation threshold to 3000 eV electron energy. For plasma physics applications, we have reported the fitting parameters of these cross sections using two different formulae for low and high energy ranges. The rate coefficients are also obtained using our calculated cross sections and considering the Maxwellian electron energy distribution function in the electron temperature range from 5 eV to 100 eV.
Citation: Atoms
PubDate: 2021-10-06
DOI: 10.3390/atoms9040076
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 77: A Missing Puzzle in Dissociative Electron
Attachment to Biomolecules: The Detection of Radicals
Authors: Sylwia Ptasinska
First page: 77
Abstract: Ionizing radiation releases a flood of low-energy electrons that often causes the fragmentation of the molecular species it encounters. Special attention has been paid to the electrons’ contribution to DNA damage via the dissociative electron attachment (DEA) process. Although numerous research groups worldwide have probed these processes in the past, and many significant achievements have been made, some technical challenges have hindered researchers from obtaining a complete picture of DEA. Therefore, this research perspective calls urgently for the implementation of advanced techniques to identify non-charged radicals that form from such a decomposition of gas-phase molecules. Having well-described DEA products offers a promise to benefit society by straddling the boundary between physics, chemistry, and biology, and it brings the tools of atomic and molecular physics to bear on relevant issues of radiation research and medicine.
Citation: Atoms
PubDate: 2021-10-07
DOI: 10.3390/atoms9040077
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 78: Triply Differential Positron and Electron Impact
Ionization of Argon: Systematic Features and Scaling
Authors: R. D. DuBois, O. G. de Lucio
First page: 78
Abstract: Triply differential data are presented for the 200 eV positron and electron impact ionization of argon. Six electron emission energies between 2.6 and 19 eV, and for scattering angles of 2, 3, and 4 degrees cover a momentum transfer range of 0.16 to 0.31 a.u. The binary and recoil intensities are fitted using a double peak structure in both regions, which, for the present kinematic conditions, are unresolved. The fitted peak intensities and angular positions are shown to have systematic dependences as a function of the momentum transfer and kinematic emission angle, respectively, and illustrate projectile charge effects. A comparison with available theories is made where it is seen that the most notable differences include the fact that for the binary lobe, the observed intensity for emission angles around 100° is absent in the theories, and the theoretical predications overestimate the importance of recoil interactions.
Citation: Atoms
PubDate: 2021-10-11
DOI: 10.3390/atoms9040078
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 79: Stereomutation in Tetracoordinate Centers via
Stabilization of Planar Tetracoordinated Systems
Authors: Komal Yadav, Upakarasamy Lourderaj, U. Deva Priyakumar
First page: 79
Abstract: The quest for stabilizing planar forms of tetracoordinate carbon started five decades ago and intends to achieve interconversion between [R]- and [S]-stereoisomers without breaking covalent bonds. Several strategies are successful in making the planar tetracoordinate form a minimum on its potential energy surface. However, the first examples of systems where stereomutation is possible were reported only recently. In this study, the possibility of neutral and dications of simple hydrocarbons (cyclopentane, cyclopentene, spiropentane, and spiropentadiene) and their counterparts with the central carbon atom replaced by elements from groups 13, 14, and 15 are explored using ab initio MP2 calculations. The energy difference between the tetrahedral and planar forms decreases from row II to row III or IV substituents. Additionally, aromaticity involving the delocalization of the lone pair on the central atom appears to help in further stabilizing the planar form compared to the tetrahedral form, especially for the row II substituents. We identified 11 systems where the tetrahedral state is a minimum on the potential energy surface, and the planar form is a transition state corresponding to stereomutation. Interestingly, the planar structures of three systems were found to be minimum, and the corresponding tetrahedral states were transition states. The energy profiles corresponding to such transitions involving both planar and tetrahedral states without the breaking of covalent bonds were examined. The systems showcased in this study and research in this direction are expected to realize molecules that experimentally exhibit stereomutation.
Citation: Atoms
PubDate: 2021-10-14
DOI: 10.3390/atoms9040079
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 80: Lowest-Order Thermal Correction to the Hydrogen
Recombination Cross-Section in Presence of Blackbody Radiation
Authors: Jaroslav Triaskin, Timur Zalialiutdinov, Aleksei Anikin, Dmitrii Solovyev
First page: 80
Abstract: In the present paper, the correction of the recombination and ionization processes of the hydrogen atom due to the thermal interaction of two charges was considered. The evaluation was based on a rigorous quantum electrodynamic (QED) approach within the framework of perturbation theory. The lowest-order radiative correction to the recombination/ionization cross-section was examined for a wide range of temperatures corresponding to laboratory and astrophysical conditions. The found thermal contribution was discussed both for specific states and for the total recombination and ionization coefficients.
Citation: Atoms
PubDate: 2021-10-14
DOI: 10.3390/atoms9040080
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 81: Polaritons in an Electron Gas—Quasiparticles
and Landau Effective Interactions
Authors: Miguel Angel Bastarrachea-Magnani, Jannie Thomsen, Arturo Camacho-Guardian, Georg M. Bruun
First page: 81
Abstract: Two-dimensional semiconductors inside optical microcavities have emerged as a versatile platform to explore new hybrid light–matter quantum states. A strong light–matter coupling leads to the formation of exciton-polaritons, which in turn interact with the surrounding electron gas to form quasiparticles called polaron-polaritons. Here, we develop a general microscopic framework to calculate the properties of these quasiparticles, such as their energy and the interactions between them. From this, we give microscopic expressions for the parameters entering a Landau theory for the polaron-polaritons, which offers a simple yet powerful way to describe such interacting light–matter many-body systems. As an example of the application of our framework, we then use the ladder approximation to explore the properties of the polaron-polaritons. Furthermore, we show that they can be measured in a non-demolition way via the light transmission/reflection spectrum of the system. Finally, we demonstrate that the Landau effective interaction mediated by electron-hole excitations is attractive leading to red shifts of the polaron-polaritons. Our work provides a systematic framework to study exciton-polaritons in electronically doped two-dimensional materials such as novel van der Waals heterostructures.
Citation: Atoms
PubDate: 2021-10-16
DOI: 10.3390/atoms9040081
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 82: Low-Energy Elastic Electron Scattering from
Helium Atoms
Authors: Robert P. McEachran, Kathryn R. Hamilton, Klaus Bartschat
First page: 82
Abstract: We reinvestigate a key process in electron-atom collision physics, the elastic scattering of electrons from helium atoms. Specifically, results from a special-purpose relativistic polarized-orbital method, which is designed to treat elastic scattering only, are compared with those from a very extensive, fully ab initio, general-purpose B-spline R-matrix (close-coupling) code.
Citation: Atoms
PubDate: 2021-10-18
DOI: 10.3390/atoms9040082
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 83: Benchmark PhotoIonization Cross-Sections of
Neutral Scandium from the Ground and Excited States
Authors: Swaraj S. Tayal, Oleg Zatsarinny
First page: 83
Abstract: The B-spline R-matrix method has been used to investigate cross-sections for photoionization of neutral scandium from the ground and excited states in the energy region from the 3d and 4s valence electron ionization thresholds to 25 eV. The initial bound states of Sc and the final residual Sc+ ionic states have been accurately calculated by combining the multiconfiguration Hartree-Fock method with the frozen-core close-coupling approach. The lowest 20 bound states of Sc I belonging to the ground 3d4s2 and excited 3d24s, 3d24p, 3d4s4p, 4s24p, and 3d3 configurations have been considered as initial states. The 81 LS final ionic states of Sc+ belonging to the terms of 3p63d2, 3p63d4l (l = 0–3), 3p63d5l (l = 0–3), 3p63d6s, 3p64s2, 3p64s4l (l = 0–3), 3p64s5l (l = 0–1), and 3p64p2 configurations have been included in the final-state close-coupling expansion. The cross-sections are dominated by complicated resonance structures in the low energy region converging to several Sc+ ionic thresholds. The inclusion of all these final ionic states has been noted to significantly impact the near-threshold resonance structures and background cross-sections. The important scattering channels for leaving the residual ion in various final states have been identified, and the 3d electron ionization channels have been noted to dominate the cross-sections at higher photon energies.
Citation: Atoms
PubDate: 2021-10-19
DOI: 10.3390/atoms9040083
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 84: Low-Energy Electron Elastic Collisions with
Actinide Atoms Am, Cm, Bk, Es, No and Lr: Negative-Ion Formation
Authors: Alfred Z. Msezane, Zineb Felfli
First page: 84
Abstract: The rigorous Regge-pole method is used to investigate negative-ion formation in actinide atoms through electron elastic total cross sections (TCSs) calculation. The TCSs are found to be characterized generally by negative-ion formations, shape resonances and Ramsauer-Townsend(R-T) minima, and they exhibit both atomic and fullerene molecular behavior near the threshold. Additionally, a polarization-induced metastable cross section with a deep R-T minimum is identified near the threshold in the Am, Cm and Bk TCSs, which flips over to a shape resonance appearing very close to the threshold in the TCSs for Es, No and Lr. We attribute these new manifestations to size effects and orbital collapse significantly impacting the polarization interaction. From the TCSs unambiguous and reliable ground, metastable and excited states negative-ion binding energies (BEs) for Am−, Cm−, Bk−, Es−, No− and Lr− anions formed during the collisions are extracted and compared with existing electron affinities (EAs) of the atoms. The novelty of the Regge-pole approach is in the extraction of the negative-ion BEs from the TCSs. We conclude that the existing theoretical EAs of the actinide atoms and the recently measured EA of Th correspond to excited anionic BEs.
Citation: Atoms
PubDate: 2021-10-19
DOI: 10.3390/atoms9040084
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 85: Targeted Cross-Section Calculations for Plasma
Simulations
Authors: Sebastian Mohr, Maria Tudorovskaya, Martin Hanicinec, Jonathan Tennyson
First page: 85
Abstract: Gathering data on electron collisions in plasmas is a vital part of conducting plasma simulations. However, data on neutral radicals and neutrals formed in the plasma by reactions between different radicals are usually not readily available. While these cross-sections can be calculated numerically, this is a time-consuming process and it is not clear from the outset which additional cross-sections are needed for a given plasma process. Hence, identifying species for which additional cross-sections are needed in advance is highly advantageous. Here, we present a structured approach to do this. In this, a chemistry set using estimated data for unknown electron collisions is run in a global plasma model. The results are used to rank the species with regard to their influence on densities of important species such as electrons or neutrals inducing desired surface processes. For this, an algorithm based on graph theory is used. The species ranking helps to make an informed decision on which cross-sections need to be calculated to improve the chemistry set and which can be neglected to save time. The validity of this approach is demonstrated through an example in an SF6/O2 plasma.
Citation: Atoms
PubDate: 2021-10-21
DOI: 10.3390/atoms9040085
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 86: Polarizabilities and Rydberg States in the
Presence of a Debye Potential
Authors: Anand Bhatia, Richard Drachman
First page: 86
Abstract: Polarizabilities and hyperpolarizabilities, α1, β1, γ1, α2, β2, γ2, α3, β3, γ3, δ and ε of hydrogenic systems have been calculated in the presence of a Debye–Huckel potential, using pseudostates for the S, P, D and F states. All of these converge very quickly as the number of terms in the pseudostates is increased and are essentially independent of the nonlinear parameters. All the results are in good agreement with the results obtained for hydrogenic systems obtained by Drachman. The effective potential seen by the outer electron is −α1/x4 + (6β1 − α2)/x6 + higher-order terms, where x is the distance from the outer electron to the nucleus. The exchange and electron–electron correlations are unimportant because the outer electron is far away from the nucleus. This implies that the conventional variational calculations are not necessary. The results agree well with the results of Drachman for the screening parameter equal to zero in the Debye–Huckel potential. We can calculate the energies of Rydberg states by using the polarizabilities and hyperpolarizabilities in the presence of Debye potential seen by the outer electron when the atoms are embedded in a plasma. Most calculations are carried out in the absence of the Debye–Huckel potential. However, it is not possible to carry out experiments when there is a complete absence of plasma at a particular electron temperature and density. The present calculations of polarizabilities and hyperpolarizabilities will provide accurate results for Rydberg states when the measurements for such states are carried out.
Citation: Atoms
PubDate: 2021-10-22
DOI: 10.3390/atoms9040086
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 87: Approximate Solution of the Thomas–Fermi
Equation for Free Positive Ions
Authors: Aleksey A. Mavrin, Alexander V. Demura
First page: 87
Abstract: The approximate solution of the nonlinear Thomas–Fermi (TF) equation for ions is found by the Fermi method. The solution is based on the new asymptotic representation of the TF ion size valid for any ionization degree. The two universal functions and their derivatives, introduced by Fermi, are calculated by recent effective algorithms for the Emden–Fowler type equations with the accuracy sufficient for majority of applications. The comparison of our results with those obtained previously shows high accuracy and validity for arbitrary values of ionization degree. This study could potentially be of interest for the statistical TF method applications in physics and chemistry.
Citation: Atoms
PubDate: 2021-10-23
DOI: 10.3390/atoms9040087
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 88: On the Accuracy of Random Phase Approximation for
Dynamical Structure Factors in Cold Atomic Gases
Authors: Patrick Kelly, Ettore Vitali
First page: 88
Abstract: Many-body physics poses one of the greatest challenges to science in the 21st century. Still more daunting is the problem of accurately calculating the properties of quantum many-body systems in the strongly correlated regime. Cold atomic gases provide an excellent test ground, for both experimentalists and theorists, to study the exotic and sometimes counterintuitive behavior of quantum many-body problems. Of particular interest is the appearance of collective excitations in these systems, such as the famous Goldstone mode and the elusive Higgs mode. It is particularly important to assess the robustness of theoretical and computational techniques to study such excitations. We build on the unprecedented opportunity provided by the fact that, in some cases, exact numerical predictions can be obtained through quantum Monte Carlo. We use these predictions to assess the accuracy of the Random Phase Approximation, which is widely considered to be a method of choice for the study of the collective excitations in a cold atomic Fermi gas modeled with a Fermi–Hubbard Hamiltonian. We found good agreement between the two methodologies for the dynamic properties, particularly for the position of the Goldstone mode. We also explored the possibility of using a renormalized, effective potential in place of the physical potential. We determined that using a renormalized potential is likely too simplistic a method for improving the accuracy of generalized Random Phase Approximation and that a more sophisticated approach is needed.
Citation: Atoms
PubDate: 2021-10-26
DOI: 10.3390/atoms9040088
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 89: BAl4Mg−/0/+: Global Minima with a Planar
Tetracoordinate or Hypercoordinate Boron Atom
Authors: Maya Khatun, Saikat Roy, Sandip Giri, Sasanka Sankhar Reddy CH, Anakuthil Anoop, Venkatesan S. Thimmakondu
First page: 89
Abstract: We have explored the chemical space of BAl4Mg−/0/+ for the first time and theoretically characterized several isomers with interesting bonding patterns. We have used chemical intuition and a cluster building method based on the tabu-search algorithm implemented in the Python program for aggregation and reaction (PyAR) to obtain the maximum number of possible stationary points. The global minimum geometries for the anion (1a) and cation (1c) contain a planar tetracoordinate boron (ptB) atom, whereas the global minimum geometry for the neutral (1n) exhibits a planar pentacoordinate boron (ppB) atom. The low-lying isomers of the anion (2a) and cation (3c) also contain a ppB atom. The low-lying isomer of the neutral (2n) exhibits a ptB atom. Ab initio molecular dynamics simulations carried out at 298 K for 2000 fs suggest that all isomers are kinetically stable, except the cation 3c. Simulations carried out at low temperatures (100 and 200 K) for 2000 fs predict that even 3c is kinetically stable, which contains a ppB atom. Various bonding analyses (NBO, AdNDP, AIM, etc.) are carried out for these six different geometries of BAl4Mg−/0/+ to understand the bonding patterns. Based on these results, we conclude that ptB/ppB scenarios are prevalent in these systems. Compared to the carbon counter-part, CAl4Mg−, here the anion (BAl4Mg−) obeys the 18 valence electron rule, as B has one electron fewer than C. However, the neutral and cation species break the rule with 17 and 16 valence electrons, respectively. The electron affinity (EA) of BAl4Mg is slightly higher (2.15 eV) than the electron affinity of CAl4Mg (2.05 eV). Based on the EA value, it is believed that these molecules can be identified in the gas phase. All the ptB/ppB isomers exhibit π/σ double aromaticity. Energy decomposition analysis predicts that the interaction between BAl4−/0/+ and Mg is ionic in all these six systems.
Citation: Atoms
PubDate: 2021-10-27
DOI: 10.3390/atoms9040089
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 90: Analytical Cross Section Approximation for
Electron Impact Ionization of Alkali and Other Metals, Inert Gases and
Hydrogen Atoms
Authors: Rusudan I. Golyatina, Sergey A. Maiorov
First page: 90
Abstract: The paper presents an analysis of data on the cross sections of electron impact ionization of atoms of alkali metals, hydrogen, noble gases, some transition metals and Al, Fe, Ni, W, Au, Hg, U. For the selected sets of experimental and theoretical data, an optimal analytical formula is found and approximation coefficients are calculated. The obtained semi-empirical formula reproduces the values of the ionization cross sections in a wide range of energies with an accuracy of the order of error of the available theoretical and experimental data.
Citation: Atoms
PubDate: 2021-10-27
DOI: 10.3390/atoms9040090
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 91: Elastic Scattering of Slow Electrons by Noble
Gases—The Effective Range Theory and the Rigid Sphere Model
Authors: Kamil Fedus
First page: 91
Abstract: We report on an extensive semi-empirical analysis of scattering cross-sections for electron elastic collision with noble gases via the Markov Chain Monte Carlo-Modified Effective Range Theory (MCMC−MERT). In this approach, the contribution of the long-range polarization potential (∼r−4) to the scattering phase shifts is precisely expressed, while the effect of the complex short-range interaction is modeled by simple quadratic expression (the so-called effective range expansion with several adjustable parameters). Additionally, we test a simple potential model of a rigid sphere combined with r−4 interaction. Both models, the MERT and the rigid sphere are based on the analytical properties of Mathieu functions, i.e., the solutions of radial Schrödinger equation with pure polarization potential. However, in contrast to MERT, the rigid sphere model depends entirely upon one adjustable parameter—the radius of a hard-core. The model’s validity is assessed by a comparative study against numerous experimental cross-sections and theoretical phase shifts. We show that this simple approach can successfully describe the electron elastic collisions with helium and neon for energies below 1 eV. The purpose of the present analysis is to give insight into the relations between the parameters of both models (that translate into the cross-sections in the very low energy range) and some “macroscopic” features of atoms such as the polarizability and atomic “radii”.
Citation: Atoms
PubDate: 2021-10-29
DOI: 10.3390/atoms9040091
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 92: Fragmentation of Identical and Distinguishable
Bosons’ Pairs and Natural Geminals of a Trapped Bosonic Mixture
Authors: Ofir E. Alon
First page: 92
Abstract: In a mixture of two kinds of identical bosons, there are two types of pairs: identical bosons’ pairs, of either species, and pairs of distinguishable bosons. In the present work, the fragmentation of pairs in a trapped mixture of Bose–Einstein condensates is investigated using a solvable model, the symmetric harmonic-interaction model for mixtures. The natural geminals for pairs made of identical or distinguishable bosons are explicitly contracted by diagonalizing the intra-species and inter-species reduced two-particle density matrices, respectively. Properties of pairs’ fragmentation in the mixture are discussed, the role of the mixture’s center-of-mass and relative center-of-mass coordinates is elucidated, and a generalization to higher-order reduced density matrices is made. As a complementary result, the exact Schmidt decomposition of the wave function of the bosonic mixture is constructed. The entanglement between the two species is governed by the coupling of their individual center-of-mass coordinates, and it does not vanish at the limit of an infinite number of particles where any finite-order intra-species and inter-species reduced density matrix per particle is 100% condensed. Implications are briefly discussed.
Citation: Atoms
PubDate: 2021-11-02
DOI: 10.3390/atoms9040092
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 93: Extreme-Ultraviolet Beam-Foil Spectra of Na
through Cl
Authors: Elmar Träbert
First page: 93
Abstract: Beam-foil EUV spectra of elements from Na through Cl are presented, partly in survey spectra and partly in detail spectra. The ionization stages of interest are medium to high, so that three to thirteen electrons remain. Research topics are outlined and the problems of the measurement technique discussed.
Citation: Atoms
PubDate: 2021-11-04
DOI: 10.3390/atoms9040093
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 94: Relativistic B-Spline R-Matrix Calculations for
Electron Scattering from Thallium Atoms
Authors: Yang Wang, Hai-Liang Du, Xi-Ming Zhu, Oleg Zatsarinny, Klaus Bartschat
First page: 94
Abstract: The Dirac B-spline R-matrix (DBSR) method is employed to treat low-energy electron collisions with thallium atoms. Special emphasis is placed on spin polarization phenomena that are investigated through calculations of the differential cross-section and the spin asymmetry function. Overall, good agreement between the present calculations and the available experimental measurements is found. The contributions of electron exchange to the spin asymmetry cannot be ignored at low impact energies, while the spin–orbit interaction plays an increasingly significant role as the impact energy rises.
Citation: Atoms
PubDate: 2021-11-05
DOI: 10.3390/atoms9040094
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 95: Analyzing the Neutron Parameters in the
Accelerator Driven Subcritical Reactor Using the Mixture of Molten Pb-Bi
as Both Target and Coolant
Authors: Tien Tran Minh
First page: 95
Abstract: In this paper, the Accelerator Driven Subcritical Reactor (ADSR) was simulated based on the structure of the TRIGA-Mark II reactor by the MCNPX program. The proton beam interacts on the Pb-Bi molten target with various energy levels from 0.5 GeV to 2.0 GeV. The important neutron parameters to evaluate the operability of ADSR were calculated as: the neutron yields according to various thicknesses of the target and according to the energy of the incident proton beam; the effective neutron multiplication factor for various fuel mixtures, along with its stability for some fuel mixtures; the axial and radial distributions of the neutron flux along with the height and radius of the core. The obtained results had shown a good agreement in using Pb-Bi molten as the interaction target and coolant for ADSR.
Citation: Atoms
PubDate: 2021-11-21
DOI: 10.3390/atoms9040095
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 96: Relativistic Configuration-Interaction and
Perturbation Theory Calculations of the Sn XV Emission Spectrum
Authors: Dmytro Filin, Igor Savukov, James Colgan
First page: 96
Abstract: Recently, there has been increased interest in developing advanced bright sources for lithography. Sn ions are particularly promising due to their bright emission spectrum in the required wavelength range. Cowan’s code has been used to model the emission; however, it has adjustable parameters, which limit its predictive power, and it has limited relativistic treatment. Here, we present calculations based on ab initio relativistic configuration-interaction many-body perturbation theory (CI-MBPT), with relativistic corrections included at the Dirac-Fock level and core-polarization effects with the second-order MBPT. As a proof of principle that the theory is generally applicable to other Sn ions with proper development, we focused on one ion where direct comparison with experimental observations is possible. The theory can also be used for ions of other elements to predict emissions for optimization of plasma-based bright sources.
Citation: Atoms
PubDate: 2021-11-22
DOI: 10.3390/atoms9040096
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 97: Total Cross Sections for Electron and Positron
Scattering on Molecules: In Search of the Dispersion Relation
Authors: Fabio Carelli, Kamil Fedus, Grzegorz Karwasz
First page: 97
Abstract: More than one hundred years of experimental and theoretical investigations of electron scattering in gases delivered cross-sections in a wide energy range, from few meV to keV. An analogy in optics, characterizing different materials, comes under the name of the dispersion relation, i.e., of the dependence of the refraction index on the light wavelength. The dispersion relation for electron (and positron) scattering was hypothesized in the 1970s, but without clear results. Here, we review experimental, theoretical, and semi-empirical cross-sections for N2, CO2, CH4, and CF4 in search of any hint for such a relation—unfortunately, without satisfactory conclusions.
Citation: Atoms
PubDate: 2021-11-22
DOI: 10.3390/atoms9040097
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 98: Evaluation of Recommended Cross Sections for the
Simulation of Electron Tracks in Water
Authors: Adrián García-Abenza, Ana I. Lozano, Juan C. Oller, Francisco Blanco, Jimena D. Gorfinkiel, Paulo Limão-Vieira, Gustavo García
First page: 98
Abstract: The accuracy of the most recent recommended cross sections dataset for electron scattering from gaseous H2O (J. Phys. Chem. Ref. Data 2021, 50, 023103) is probed in a joint experimental and computational study. Simulations of the magnetically confined electron transport through a gas cell containing H2O for different beam energies (3, 10 and 70 eV) and pressures (2.5 to 20.0 mTorr) have been performed by using a specifically designed Monte Carlo code. The simulated results have been compared with the corresponding experimental data as well as with simulations performed with Geant4DNA. The comparison made between the experiment and simulation provides insight into possible improvement of the recommended dataset.
Citation: Atoms
PubDate: 2021-11-22
DOI: 10.3390/atoms9040098
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 99: Binary-Encounter Model for Direct Ionization of
Molecules by Positron-Impact
Authors: Małgorzata Franz, Katarzyna Wiciak-Pawłowska, Jan Franz
First page: 99
Abstract: We introduce two models for the computation of direct ionization cross sections by positron impact over a wide range of collision energies. The models are based on the binary-encounter-Bethe model and take into account an extension of the Wannier theory. The cross sections computed with these models show good agreement with experimental data. The extensions improve the agreement between theory and experiment for collision energies between the first ionization threshold and the peak of the cross section. The models are based on a small set of parameters, which can be computed with standard quantum chemistry program packages.
Citation: Atoms
PubDate: 2021-11-24
DOI: 10.3390/atoms9040099
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 100: Population Kinetics Modeling of Low-Temperature
Argon Plasma
Authors: Hyun-Kyung Chung, Mi-Young Song, Ji-Won Kwon, Myeong-Geon Lee, Jihoon Park, Namjae Bae, Jeamin Song, Gon-Ho Kim, Dipti, Yuri Ralchenko
First page: 100
Abstract: Optical emission spectroscopy has been widely used in low-temperature argon plasma diagnostics. A coronal model is usually used to analyze the measured line ratios for diagnostics with a single temperature and density. However, many plasma processing conditions deviate from single temperature and density, optically thin conditions, or even coronal plasma conditions due to cascades from high-lying states. In this paper, we present a collisional-radiative model to investigate the validity of coronal approximations over a range of plasma conditions of Te = 1–4 eV and Ne = 108–1013 cm−3. The commonly used line ratios are found to change from a coronal limit where they are independent of Ne to a collisional-radiative regime where they are not. The effects of multiple-temperature plasma, radiation trapping, wall neutralization, and quenching on the line ratios are investigated to identify the plasma conditions under which these effects are significant. This study demonstrates the importance of the completeness of atomic datasets in applying a collisional-radiative model to low-temperature plasma diagnostics.
Citation: Atoms
PubDate: 2021-11-24
DOI: 10.3390/atoms9040100
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 101: On the Feasibility of Rovibrational Laser
Cooling of Radioactive RaF+ and RaH+ Cations
Authors: Timur A. Isaev, Shane G. Wilkins, Michail Athanasakis-Kaklamanakis
First page: 101
Abstract: Polar radioactive molecules have been suggested to be exceptionally sensitive systems in the search for signatures of symmetry-violating effects in their structure. Radium monofluoride (RaF) possesses an especially attractive electronic structure for such searches, as the diagonality of its Franck-Condon matrix enables the implementation of direct laser cooling for precision experiments. To maximize the sensitivity of experiments with short-lived RaF isotopologues, the molecular beam needs to be cooled to the rovibrational ground state. Due to the high kinetic energies and internal temperature of extracted beams at radioactive ion beam (RIB) facilities, in-flight rovibrational cooling would be restricted by a limited interaction timescale. Instead, cooling techniques implemented on ions trapped within a radiofrequency quadrupole cooler-buncher can be highly efficient due to the much longer interaction times (up to seconds). In this work, the feasibility of rovibrationally cooling trapped RaF+ and RaH+ cations with repeated laser excitation is investigated. Due to the highly diagonal nature between the ionic ground state and states in the neutral system, any reduction of the internal temperature of the molecular ions would largely persist through charge-exchange without requiring the use of cryogenic buffer gas cooling. Quasirelativistic X2C and scalar-relativistic ECP calculations were performed to calculate the transition energies to excited electronic states and to study the nature of chemical bonding for both RaF+ and RaH+. The results indicate that optical manipulation of the rovibrational distribution of trapped RaF+ and RaH+ is unfeasible due to the high electronic transition energies, which lie beyond the capabilities of modern laser technology. However, more detailed calculations of the structure of RaH+ might reveal possible laser-cooling pathways.
Citation: Atoms
PubDate: 2021-11-26
DOI: 10.3390/atoms9040101
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 102: Excitation of the 6d 2D → 6p 2Po
Radiative Transitions in the Pb+ Ion by Electron Impact
Authors: Viktoriya Roman, Valdas Jonauskas, Sigitas Kučas, Anna Gomonai, Aleksandr Gomonai, Yuriy Hutych
First page: 102
Abstract: Results of experimental and theoretical investigation of electron-impact excitation of the 6s26d D2→6s26p P2o spectral transitions from the ground 6s26p P21/2o level in the Pb+ ion are presented. The experimental excitation functions for the transitions, measured by a VUV spectroscopy method, using the crossed electron and ion beams technique, reveal a rather distinct resonance structure resulting mainly from the electron decay of both atomic and ionic autoionizing states. The absolute values of the emission cross-sections, obtained by normalizing the experimental data at the incident electron energy 100 eV by those calculated using the Flexible Atomic Code software package, were found to be (0.35 ± 0.17) × 10–16 cm2 for the 6s26d D23/2 → 6s26p P21/2o (λ143.4 nm) transition and (0.19 ± 0.09) × 10–16 cm2 for the 6s26d D25/2 → 6s26p P23/2o (λ182.2 nm) transition.
Citation: Atoms
PubDate: 2021-11-29
DOI: 10.3390/atoms9040102
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 103: Electron Scattering Cross-Section Calculations
for Atomic and Molecular Iodine
Authors: Harindranath Ambalampitiya, Kathryn Hamilton, Oleg Zatsarinny, Klaus Bartschat, Matt Turner, Anna Dzarasova, Jonathan Tennyson
First page: 103
Abstract: Cross sections for electron scattering from atomic and molecular iodine are calculated based on the R-matrix (close-coupling) method. Elastic and electronic excitation cross sections are presented for both I and I2. The dissociative electron attachment and vibrational excitation cross sections of the iodine molecule are obtained using the local complex potential approximation. Ionization cross sections are also computed for I2 using the BEB model.
Citation: Atoms
PubDate: 2021-11-30
DOI: 10.3390/atoms9040103
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 104: Relativistic Configuration-Interaction and
Perturbation Theory Calculations for Heavy Atoms
Authors: Igor M. Savukov, Dmytro Filin, Pinghan Chu, Michael W. Malone
First page: 104
Abstract: Heavy atoms present challenges to atomic theory calculations due to the large number of electrons and their complicated interactions. Conventional approaches such as calculations based on Cowan’s code are limited and require a large number of parameters for energy agreement. One promising approach is relativistic configuration-interaction and many-body perturbation theory (CI-MBPT) methods. We present CI-MBPT results for various atomic systems where this approach can lead to reasonable agreement: La I, La II, Th I, Th II, U I, Pu II. Among atomic properties, energies, g-factors, electric dipole moments, lifetimes, hyperfine structure constants, and isotopic shifts are discussed. While in La I and La II accuracy for transitions is better than that obtained with other methods, more work is needed for actinides.
Citation: Atoms
PubDate: 2021-11-30
DOI: 10.3390/atoms9040104
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 105: Time Delay in Electron Collision with a
Spherical Target as a Function of the Scattering Angle
Authors: Miron Ya. Amusia, Arkadiy S. Baltenkov, Igor Woiciechowski
First page: 105
Abstract: We have studied the angular time delay in slow-electron elastic scattering by spherical targets as well as the average time delay of electrons in this process. It is demonstrated how the angular time delay is connected to the Eisenbud–Wigner–Smith (EWS) time delay. The specific features of both angular and energy dependencies of these time delays are discussed in detail. The potentialities of the derived general formulas are illustrated by the numerical calculations of the time delays of slow electrons in the potential fields of both absolutely hard-sphere and delta-shell potential well of the same radius. The conducted studies shed more light on the specific features of these time delays.
Citation: Atoms
PubDate: 2021-12-01
DOI: 10.3390/atoms9040105
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 106: Emergence of Anyons on the Two-Sphere in
Molecular Impurities
Authors: Morris Brooks, Mikhail Lemeshko, Douglas Lundholm, Enderalp Yakaboylu
First page: 106
Abstract: Recently it was shown that anyons on the two-sphere naturally arise from a system of molecular impurities exchanging angular momentum with a many-particle bath (Phys. Rev. Lett. 126, 015301 (2021)). Here we further advance this approach and rigorously demonstrate that in the experimentally realized regime the lowest spectrum of two linear molecules immersed in superfluid helium corresponds to the spectrum of two anyons on the sphere. We develop the formalism within the framework of the recently experimentally observed angulon quasiparticle.
Citation: Atoms
PubDate: 2021-12-02
DOI: 10.3390/atoms9040106
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 107: Oleg Zatsarinny: Expert Atomic Theorist, Kind
Man
Authors: Thomas W. Gorczyca
First page: 107
Abstract: I met Oleg Zatsarinny in 2001, and he then worked with me at Western Michigan University for two years. From 2003 to 2013, we were coauthors of 15 papers on theoretical atomic physics, and maintained a friendly relationship over twenty years, meeting and socializing often at conferences. Further elaboration follows below.
Citation: Atoms
PubDate: 2021-12-03
DOI: 10.3390/atoms9040107
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 108: Circular Dichroism in the Photoionization of
Unpolarized Atoms by Two Crossing Photon Beams
Authors: Alexei V. Meremianin, Nikolai L. Manakov
First page: 108
Abstract: The polarization dependence of the photoionization probability was analyzed in the case when a randomly oriented atom is irradiated by two crossing polarized monochromatic photon beams with the same frequency. It was found that the angular distributions of photoelectrons exhibit the effect of circular dichroism (CD), which consists of the dependence of the photoionization probability on the sign of the circular polarization degree of each beam. We demonstrate that the CD effect exists only for coherent crossing photon beams. It was shown that CD effects are strongly dependent on the phase difference between the electric field vectors of the photon beams and have a quite large magnitude. The possibilities of the experimental observation of CD effects are discussed.
Citation: Atoms
PubDate: 2021-12-03
DOI: 10.3390/atoms9040108
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 109: Oleg Zatsarinny (1953–2021): Memories
by His Colleagues
Authors: Klaus Bartschat, Charlotte Froese Fischer, Alexei N. Grum-Grzhimailo
First page: 109
Abstract: A collection of short stories about Oleg Ivanovich Zatsarinny (1953–2021) to whom this Special Issue of Atoms is dedicated.
Citation: Atoms
PubDate: 2021-12-07
DOI: 10.3390/atoms9040109
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 110: Asymmetric Lineshapes of Efimov Resonances in
Mass-Imbalanced Ultracold Gases
Authors: Panagiotis Giannakeas, Chris H. Greene
First page: 110
Abstract: The resonant profile of the rate coefficient for three-body recombination into a shallow dimer is investigated for mass-imbalanced systems. In the low-energy limit, three atoms collide with zero-range interactions, in a regime where the scattering lengths of the heavy–heavy and the heavy–light subsystems are positive and negative, respectively. For this physical system, the adiabatic hyperspherical representation is combined with a fully semi-classical method and we show that the shallow dimer recombination spectra display an asymmetric lineshape that originates from the coexistence of Efimov resonances with Stückelberg interference minima. These asymmetric lineshapes are quantified utilizing the Fano profile formula. In particular, a closed-form expression is derived that describes the width of the corresponding Efimov resonances and the Fano lineshape asymmetry parameter q. The profile of Efimov resonances exhibits a q-reversal effect as the inter- and intra-species scattering lengths vary. In the case of a diverging asymmetry parameter, i.e., q →∞, we show that the Efimov resonances possess zero width and are fully decoupled from the three-body and atom–dimer continua, and the corresponding Efimov metastable states behave as bound levels.
Citation: Atoms
PubDate: 2021-12-07
DOI: 10.3390/atoms9040110
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 111: Special Issue “Interaction of Ionizing
Photons with Atomic and Molecular Ions”
Authors: Eugene T. Kennedy, John T. Costello, Jean-Paul Mosnier
First page: 111
Abstract: The interaction of ionizing photons with atoms or ions is a fundamental process in nature, with laboratory, atmospheric and astrophysical implications [...]
Citation: Atoms
PubDate: 2021-12-13
DOI: 10.3390/atoms9040111
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 112: One-Dimensional Disordered Bosonic Systems
Authors: Chiara D’Errico, Marco G. Tarallo
First page: 112
Abstract: Disorder is everywhere in nature and it has a fundamental impact on the behavior of many quantum systems. The presence of a small amount of disorder, in fact, can dramatically change the coherence and transport properties of a system. Despite the growing interest in this topic, a complete understanding of the issue is still missing. An open question, for example, is the description of the interplay of disorder and interactions, which has been predicted to give rise to exotic states of matter such as quantum glasses or many-body localization. In this review, we will present an overview of experimental observations with disordered quantum gases, focused on one-dimensional bosons, and we will connect them with theoretical predictions.
Citation: Atoms
PubDate: 2021-12-14
DOI: 10.3390/atoms9040112
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 113: Study of Positron Impact Scattering from Methane
and Silane Using an Analytically Obtained Static Potential with
Correlation Polarization
Authors: Dibyendu Mahato, Lalita Sharma, Rajesh Srivastava
First page: 113
Abstract: A detailed study of positron impact elastic scattering from methane and silane is carried out using a model potential consisting of static and polarization potentials. The static potential for the molecular target is obtained analytically by using accurate Gaussian molecular wavefunctions. The molecular orbitals are expressed as a linear combination of Gaussian atomic orbitals. Along with the analytically obtained static potential, a correlation polarization potential is also added to construct the model potential. Utilizing the model potential, the Schrödinger equation is solved using the partial wave phase shift analysis method, and the scattering amplitude is obtained in terms of the phase shifts. Thereafter, the differential, integrated and total cross sections are calculated. These cross-section results are compared with the previously reported measurements and theoretical calculations.
Citation: Atoms
PubDate: 2021-12-14
DOI: 10.3390/atoms9040113
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 114: Mechanisms of 1s Double-Core-Hole Excitation and
Decay in Neon
Authors: Maksim Kiselev, Elena Gryzlova, Sergei Burkov, Oleg Zatsarinny, Alexei Grum-Grzhimailo
First page: 114
Abstract: The formation and decay of double-core-hole (DCH) states of the neon ion irradiated by an intense electromagnetic x-ray field are studied theoretically. In the present research DCH formation is the result of sequential absorption of two photons with the creation of an intermediate ion. Detailed calculations of the partial decays and probabilities of shake-ups at the atomic and ionic ionization stages are presented. The angular distribution of photoelectrons corresponding to various residual ionic states are calculated. Specifically, we predict the lack of any photoelectrons corresponding to the residual ionic state 1s12s22pnmpn′2Sf+1D in the direction of the electric field polarization. Dynamical competition between single-core-hole state decay and excitation is analyzed and pulse parameters corresponding to various dynamical regimes are found.
Citation: Atoms
PubDate: 2021-12-19
DOI: 10.3390/atoms9040114
Issue No: Vol. 9, No. 4 (2021)
- Atoms, Vol. 9, Pages 65: In Silico Studies on Selected Neutral Molecules,
CGa2Ge2, CAlGaGe2, and CSiGa2Ge Containing Planar Tetracoordinate Carbon
Authors: Prasenjit Das, Pratim Kumar Chattaraj
First page: 65
Abstract: Density functional theory (DFT) was used to study the structure, stability, and bonding in some selected neutral pentaatomic systems, viz., CGa2Ge2, CAlGaGe2, and CSiGa2Ge containing planar tetracoordinate carbon. The systems are kinetically stable, as predicted from the ab initio molecular dynamics simulations. The natural bond orbital (NBO) analysis showed that strong electron donation occurs to the central planar carbon atom by the peripheral atoms in all the studied systems. From the nucleus independent chemical shift (NICS) analysis, it is shown that the systems possess both σ- and π- aromaticity. The presence of 18 valence electrons in these systems, in their neutral form, appears to be important for their stability with planar geometries rather than tetrahedral structures. The nature of bonding is understood through the adaptive natural density partitioning analysis (AdNDP), quantum theory of atoms in molecules (QTAIM) analysis, and also via Wiberg bond index (WBI) and electron localization function (ELF).
Citation: Atoms
PubDate: 2021-09-10
DOI: 10.3390/atoms9030065
Issue No: Vol. 9, No. 3 (2021)
- Atoms, Vol. 9, Pages 66: Revealing the Target Electronic Structure with
Under-Threshold RABBIITT
Authors: Anatoli Kheifets
First page: 66
Abstract: The process of reconstruction of attosecond beating by interference of two-photon transitions (RABBITT) reveals the target atom electronic structure when one of the transitions proceeds from below the ionization threshold. Such an under-threshold RABBITT resonates with the target bound states and thus maps faithfully the discrete energy levels and the corresponding oscillator strengths. We demonstrate this sensitivity by considering the Ne atom driven by the combination of the XUV and IR pulses at the fundmanetal laser frequency in the 800 and 1000 nm ranges.
Citation: Atoms
PubDate: 2021-09-13
DOI: 10.3390/atoms9030066
Issue No: Vol. 9, No. 3 (2021)
- Atoms, Vol. 9, Pages 67: Simultaneous Excitation of Helium by Means of an
Electron and a Photon: A Joined Experimental and Theoretical Study
Authors: Imane Ajana, Driss Nehari, Driss Khalil, Abdelmalek Taoutioui, Hicham Agueny, Abdelkader Makhoute
First page: 67
Abstract: We report on a joined experimental and theoretical study of differential cross-sections resulting from inelastic scattering of a monoenergetic electron by helium atoms in the presence of an intense carbon dioxide laser. In particular, we measured the signals of the scattered electrons during the simultaneous electron–photon excitation of He 21P state for the first three microseconds of the laser pulse. The signals were measured for an incident electron energy of 45 eV and showed a structure that emerged at small scattering angles. The latter was found to be sensitive to the nature of the transferred photons, as well as the intensity of the laser field. The experimental findings were supported by quantum calculations based on the second-order Born approximation in which the correlated electron–electron interactions were taken into account.
Citation: Atoms
PubDate: 2021-09-17
DOI: 10.3390/atoms9030067
Issue No: Vol. 9, No. 3 (2021)
- Atoms, Vol. 9, Pages 68: Three-Photon Ionization with One-Photon Resonance
between Excited Levels
Authors: Gomonai, Remeta, Gomonai
First page: 68
Abstract: Within the framework of a three-level model, the process of three-photon ionization with one-photon resonance between two excited levels (with the lower one being initially unpopulated) is considered using the density matrix method. It is shown that such resonance can result in the appearance of a maximum in the three-photon ionization spectrum when detuning between the resonance wavenumber and the wavenumber of the transition responsible for the lower excited level being populated exceeds the laser radiation linewidth by more than three orders of magnitude.
Citation: Atoms
PubDate: 2021-09-17
DOI: 10.3390/atoms9030068
Issue No: Vol. 9, No. 3 (2021)
- Atoms, Vol. 9, Pages 69: Simultaneous Observation of Tungsten Spectra of
W0 to W46+ Ions in Visible, VUV and EUV Wavelength Ranges in the Large
Helical Device
Authors: Oishi, Morita, Kato, Murakami, Sakaue, Kawamoto, Kawate, Goto
First page: 69
Abstract: Spectroscopic studies for emissions released from tungsten ions have been conducted in the Large Helical Device (LHD) for contribution to the tungsten transport study in tungsten divertor fusion devices and for expansion of the experimental database of tungsten line emissions. Tungsten ions are distributed in the LHD plasma by injecting a pellet consisting of a small piece of tungsten metal wire enclosed by a carbon tube. Line emissions from W0, W5+, W6+, W24+–W28+, W37+, W38+, and W41+–W46+ are observed simultaneously in the visible (3200–3550 Å), vacuum ultraviolet (250–1050 Å), and extreme ultraviolet (5–300 Å) wavelength ranges and the wavelengths are summarized. Temporal evolutions of line emissions from these charge states are compared for comprehensive understanding of tungsten impurity behavior in a single discharge. The charge distribution of tungsten ions strongly depends on the electron temperature. Measurements of emissions from W10+ to W20+ are still insufficient, which is addressed as a future task.
Citation: Atoms
PubDate: 2021-09-17
DOI: 10.3390/atoms9030069
Issue No: Vol. 9, No. 3 (2021)
- Atoms, Vol. 10, Pages 1: Magic Wavelengths for 1S–nS and 2S–nS
Transitions in Hydrogenlike Systems
Authors: Chandra M. Adhikari, Jonathan C. Canales, Thusitha P. W. Arthanayaka, Ulrich D. Jentschura
First page: 1
Abstract: We study the magic wavelength for two-photon 1S–nS transitions in a hydrogen and deuterium atom, as well as 2S–nS transitions, where the lower level is the metastable 2S state. At the magic wavelength, the dynamic Stark shifts of the ground and the excited state of the transition coincide, so that the transition frequency is independent of the intensity of the trapping laser field. Experimentally feasible magic wavelengths of transitions with small slopes in the atomic polarizabilities are determined; these are the most stable magic wavelengths against variations of the laser frequency. We provide data for the magic wavelengths for the 1S–nS and 2S–nS transitions in hydrogen and deuterium, with n=2,⋯,8. We also analyze the stability of the elimination of the ac Stark shift at the magic wavelength against tiny variations of the trapping laser frequency from the magic value.
Citation: Atoms
PubDate: 2021-12-22
DOI: 10.3390/atoms10010001
Issue No: Vol. 10, No. 1 (2021)
- Atoms, Vol. 10, Pages 2: Electron Impact Ionization of Metastable States
of Diatomic Molecules
Authors: Annarita Laricchiuta, Roberto Celiberto, Gianpiero Colonna
First page: 2
Abstract: The Binary-Encounter Bethe approach was applied to the estimation of total ionization induced by electron impact in metastable states of diatomic molecules. The cross sections recently obtained for N2 and CO are reviewed and the new results for H2 are presented, discussing their reliability through the comparison with other theoretical methods.
Citation: Atoms
PubDate: 2021-12-22
DOI: 10.3390/atoms10010002
Issue No: Vol. 10, No. 1 (2021)
- Atoms, Vol. 10, Pages 3: Pattern Formation in One-Dimensional Polaron
Systems and Temporal Orthogonality Catastrophe
Authors: Georgios M. Koutentakis, Simeon I. Mistakidis, Peter Schmelcher
First page: 3
Abstract: Recent studies have demonstrated that higher than two-body bath-impurity correlations are not important for quantitatively describing the ground state of the Bose polaron. Motivated by the above, we employ the so-called Gross Ansatz (GA) approach to unravel the stationary and dynamical properties of the homogeneous one-dimensional Bose-polaron for different impurity momenta and bath-impurity couplings. We explicate that the character of the equilibrium state crossovers from the quasi-particle Bose polaron regime to the collective-excitation stationary dark-bright soliton for varying impurity momentum and interactions. Following an interspecies interaction quench the temporal orthogonality catastrophe is identified, provided that bath-impurity interactions are sufficiently stronger than the intraspecies bath ones, thus generalizing the results of the confined case. This catastrophe originates from the formation of dispersive shock wave structures associated with the zero-range character of the bath-impurity potential. For initially moving impurities, a momentum transfer process from the impurity to the dispersive shock waves via the exerted drag force is demonstrated, resulting in a final polaronic state with reduced velocity. Our results clearly demonstrate the crucial role of non-linear excitations for determining the behavior of the one-dimensional Bose polaron.
Citation: Atoms
PubDate: 2021-12-28
DOI: 10.3390/atoms10010003
Issue No: Vol. 10, No. 1 (2021)
- Atoms, Vol. 10, Pages 4: Accurate Exponential Representations for the
Ground State Wave Functions of the Collinear Two-Electron Atomic Systems
Authors: Evgeny Z. Liverts, Nir Barnea
First page: 4
Abstract: In the framework of the study of helium-like atomic systems possessing the collinear configuration, we propose a simple method for computing compact but very accurate wave functions describing the relevant S-state. It is worth noting that the considered states include the well-known states of the electron–nucleus and electron–electron coalescences as a particular case. The simplicity and compactness imply that the considered wave functions represent linear combinations of a few single exponentials. We have calculated such model wave functions for the ground state of helium and the two-electron ions with nucleus charge 1≤Z≤5. The parameters and the accompanying characteristics of these functions are presented in tables for number of exponential from 3 to 6. The accuracy of the resulting wave functions are confirmed graphically. The specific properties of the relevant codes by Wolfram Mathematica are discussed. An example of application of the compact wave functions under consideration is reported.
Citation: Atoms
PubDate: 2021-12-29
DOI: 10.3390/atoms10010004
Issue No: Vol. 10, No. 1 (2021)
- Atoms, Vol. 10, Pages 5: Excitations of the nS States of Atomic Hydrogen
by Electron Impact, Excitation Rate Coefficients, and Phase Shifts:
Comparison with Positron Impact Excitation
Authors: Anand K. Bhatia
First page: 5
Abstract: The excitation cross-sections of the nS states of atomic hydrogen, n = 2 to 6, by electron impact on the ground state of atomic hydrogen were calculated using the variational polarized-orbital method at various incident electron energies in the range 10 to 122 eV. Converged excitation cross-sections were obtained using sixteen partial waves (L = 0 to 15). Excitation cross-sections to 2S state, calculated earlier, were calculated at higher energies than before. Results obtained using the hybrid theory (variational polarized orbital method) are compared to those obtained using other approaches such as the Born–Oppenheimer, close-coupling, R-matrix, and complex-exterior scaling methods using only the spherical symmetric wave functions. Phase shifts and elastic cross-sections are given at various energies and angular momenta. Excitation rate coefficients were calculated at various electron temperatures, which are required for plasma diagnostics in solar and astrophysics to infer plasma parameters. Excitation cross-sections are compared with those obtained by positron impact excitation.
Citation: Atoms
PubDate: 2021-12-31
DOI: 10.3390/atoms10010005
Issue No: Vol. 10, No. 1 (2021)