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  This is an Open Access Journal Open Access journal
   ISSN (Online) 2218-2004
   Published by MDPI Homepage  [156 journals]
  • Atoms, Vol. 5, Pages 34: Effect of Turbulence on Line Shapes in
           Astrophysical and Fusion Plasmas

    • Authors: Ibtissem Hannachi, Mutia Meireni, Paul Génésio, Joël Rosato, Roland Stamm, Yannick Marandet
      First page: 34
      Abstract: We look at the effect of wave collapse turbulence on a hydrogen line shape in plasma. An atom immersed in plasma affected by strong Langmuir turbulence may be perturbed by a sequence of wave packets with a maximum electric field magnitude that is larger than the Holtsmark field. For such conditions, we propose to calculate the shape of the hydrogen Lyman α Lyman β and Balmer α lines with a numerical integration of the Schrödinger equation coupled to a simulation of a sequence of electric fields modeling the effects of the Langmuir wave. We present and discuss several line profiles of Lyman and Balmer lines.
      Citation: Atoms
      PubDate: 2017-09-25
      DOI: 10.3390/atoms5040034
      Issue No: Vol. 5, No. 4 (2017)
  • Atoms, Vol. 5, Pages 35: Line Shape Modeling for the Diagnostic of the
           Electron Density in a Corona Discharge

    • Authors: Joël Rosato, Nelly Bonifaci, Zhiling Li, Roland Stamm
      First page: 35
      Abstract: We present an analysis of spectra observed in a corona discharge designed for the study of dielectrics in electrical engineering. The medium is a gas of helium and the discharge was performed at the vicinity of a tip electrode under high voltage. The shape of helium lines is dominated by the Stark broadening due to the plasma microfield. Using a computer simulation method, we examine the sensitivity of the He 492 nm line shape to the electron density. Our results indicate the possibility of a density diagnostic based on passive spectroscopy. The influence of collisional broadening due to interactions between the emitters and neutrals is discussed.
      Citation: Atoms
      PubDate: 2017-09-28
      DOI: 10.3390/atoms5040035
      Issue No: Vol. 5, No. 4 (2017)
  • Atoms, Vol. 5, Pages 36: Stark-Zeeman Line Shape Modeling for Magnetic
           White Dwarf and Tokamak Edge Plasmas: Common Challenges

    • Authors: Joël Rosato, Ny Kieu, Ibtissem Hannachi, Mohammed Koubiti, Yannick Marandet, Roland Stamm, Milan S. Dimitrijević, Zoran Simić
      First page: 36
      Abstract: The shape of atomic spectral lines in plasmas contains information on the plasma parameters, and can be used as a diagnostic tool. Under specific conditions, the plasma located at the edge of tokamaks has parameters similar to those in magnetic white dwarf stellar atmospheres, which suggests that the same line shape models can be used. A problem common to tokamak and magnetic white dwarfs concerns the modeling of Stark broadening of hydrogen lines in the presence of an external magnetic field and the related Zeeman effect. In this work, we focus on a selection of issues relevant to Stark broadening in magnetized hydrogen plasmas. Various line shape models are presented and discussed through applications to ideal cases.
      Citation: Atoms
      PubDate: 2017-10-04
      DOI: 10.3390/atoms5040036
      Issue No: Vol. 5, No. 4 (2017)
  • Atoms, Vol. 5, Pages 37: Discrepancies in Atomic Data and Suggestions for
           Their Resolutions

    • Authors: Kanti Aggarwal
      First page: 37
      Abstract: The analysis and modelling of a range of plasmas (for example, astrophysical, laser- produced and fusion) require atomic data for a number of parameters, such as energy levels, radiative rates and electron impact excitation rates, or equivalently, the effective collision strengths. Such data are desired for a wide range of elements and their many ions, although all elements are not useful for all types of plasmas. Since measurements of atomic data are mostly confined to only a few energy levels of some ions, calculations for all parameters are highly important. However, often, there are large discrepancies among different calculations for almost all parameters, which makes it difficult to apply the data with confidence. Many such discrepancies (and the possible remedies) were discussed earlier (Fusion Sci. Technol. 2013, 63, 363). Since then, many more anomalies for almost all of these atomic parameters have been noticed. Therefore, this paper is a revisit of various atomic parameters to highlight the large discrepancies, their possible sources and some suggestions to avoid these, so that comparatively more accurate and reliable atomic data may be available in the future.
      Citation: Atoms
      PubDate: 2017-10-09
      DOI: 10.3390/atoms5040037
      Issue No: Vol. 5, No. 4 (2017)
  • Atoms, Vol. 5, Pages 38: THz/Infrared Double Resonance Two-Photon
           Spectroscopy of HD+ for Determination of Fundamental Constants

    • Authors: Florin Constantin
      First page: 38
      Abstract: A double resonance two-photon spectroscopy scheme is discussed to probe jointly rotational and rovibrational transitions of ensembles of trapped HD+ ions. The two-photon transition rates and lightshifts are calculated with the two-photon tensor operator formalism. The rotational lines may be observed with sub-Doppler linewidth at the hertz level and good signal-to-noise ratio, improving the resolution in HD+ spectroscopy beyond the 10−12 level. The experimental accuracy, estimated at the 10−12 level, is comparable with the accuracy of theoretical calculations of HD+ energy levels. An adjustment of selected rotational and rovibrational HD+ lines may add clues to the proton radius puzzle, may provide an independent determination of the Rydberg constant, and may improve the values of proton-to-electron and deuteron-to-proton mass ratios beyond the 10−11 level.
      Citation: Atoms
      PubDate: 2017-10-12
      DOI: 10.3390/atoms5040038
      Issue No: Vol. 5, No. 4 (2017)
  • Atoms, Vol. 5, Pages 24: Spectrum of Singly Charged Uranium (U II) :
           Theoretical Interpretation of Energy Levels, Partition Function and
           Classified Ultraviolet Lines

    • Authors: Ali Meftah, Mourad Sabri, Jean-François Wyart, Wan-Ü Tchang-Brillet
      First page: 24
      Abstract: In an attempt to improve U II analysis, the lowest configurations of both parities have been interpreted by means of the Racah-Slater parametric method, using Cowan codes. In the odd parity, including the ground state, 253 levels of the interacting configurations 5 f 3 7 s 2 + 5 f 3 6 d 7 s + 5 f 3 6 d 2 + 5 f 4 7 p + 5 f 5 are interpreted by 24 free parameters and 64 constrained ones, with a root mean square (rms) deviation of 60 cm − 1 . In the even parity, the four known configurations 5 f 4 7 s , 5 f 4 6 d , 5 f 2 6 d 2 7 s , 5 f 2 6 d 7 s 2 and the unknown 5 f 2 6 d 3 form a basis for interpreting 125 levels with a rms deviation of 84 cm − 1 . Due to perturbations, the theoretical description of the higher configurations 5 f 3 7 s 7 p + 5 f 3 6 d 7 p remains unsatisfactory. The known and predicted levels of U II are used for a determination of the partition function. The parametric study led us to a re-investigation of high resolution ultraviolet spectrum of uranium recorded at the Meudon Observatory in the late eighties, of which the analysis was unachieved. In the course of the present study, a number of 451 lines of U II has been classified in the region 2344 –2955 Å. One new level has been established as 5 f 3 6 d 7 p ( 4 I ) 6 K ( J = 5.5 ) at 39113.98 ± 0.1 cm − 1 .
      PubDate: 2017-06-26
      DOI: 10.3390/atoms5030024
      Issue No: Vol. 5, No. 3 (2017)
  • Atoms, Vol. 5, Pages 25: Wavelengths of the Self-Photopumped Nickel-Like
           4f 1P1→4d 1P1 X-ray Laser Transitions

    • Authors: Elena Ivanova
      First page: 25
      Abstract: The energies for the lower 3d3/24d3/2 [J = 1] and upper 3d3/24f5/2 [J = 1] working levels in the self-photopumped X-ray laser are analyzed along the Ni-like sequence. We have found some irregularities in these energy levels in the range Z = 42–49. The causes of the irregularities are studied. The list of elements that lase on the self-photopumped transition can be extended much further than originally known. We calculate the wavelengths of this transition in Ni-like sequence to Z = 79 using the relativistic perturbation theory with a zero approximation model potential. We estimate the wavelength accuracy for Z > 50 as Δλ/λ ≤ 0.005.
      Citation: Atoms
      PubDate: 2017-07-13
      DOI: 10.3390/atoms5030025
      Issue No: Vol. 5, No. 3 (2017)
  • Atoms, Vol. 5, Pages 26: Stark Widths of Ar II Spectral Lines in the
           Atmospheres of Subdwarf B Stars

    • Authors: Rafik Hamdi, Nabil Ben Nessib, Sylvie Sahal Bréchot, Milan Dimitrijević
      First page: 26
      Abstract: Stark broadening parameters are of interest for many problems in astrophysics and laboratory plasmas investigation. Ar II spectral lines are observed in many kinds of stellar atmospheres such as the atmospheres of B-Type stars and subdwarf B stars. In this work, we present theoretical Stark widths for Ar II spectral lines. We use the impact semiclassical perturbation approach. Our results are compared with the available experimental values. Finally, the importance of the Stark broadening mechanism is studied in atmospheric conditions of subdwarf B stars.
      Citation: Atoms
      PubDate: 2017-09-07
      DOI: 10.3390/atoms5030026
      Issue No: Vol. 5, No. 3 (2017)
  • Atoms, Vol. 5, Pages 27: Semiclassical Stark Broadening Parameters of Ar
           VII Spectral Lines

    • Authors: Milan Dimitrijević, Aleksandar Valjarević, Sylvie Sahal-Bréchot
      First page: 27
      Abstract: Using the semi-classical perturbation approach in the impact approximation, full width at half maximum and shift have been determined for eight spectral lines of Ar VII, for broadening by electron-, proton-, and He III-impacts. The results are provided for temperatures from 20,000 K to 500,000 K, and for an electron density of 10 18 cm − 3 . The obtained results will be included in the STARK-B database, which is also in the virtual atomic and molecular data center (VAMDC).
      Citation: Atoms
      PubDate: 2017-09-08
      DOI: 10.3390/atoms5030027
      Issue No: Vol. 5, No. 3 (2017)
  • Atoms, Vol. 5, Pages 28: Radiative Decay Rates for Electric Dipole,
           Magnetic Dipole and Electric Quadrupole Transitions in Triply Ionized
           Thulium (Tm IV)

    • Authors: Saturnin Enzonga Yoca, Pascal Quinet
      First page: 28
      Abstract: A new set of radiative decay parameters (oscillator strengths, transition probabilities) for spectral lines in triply ionized thulium (Tm IV) has been obtained within the framework of the pseudo-relativistic Hartree-Fock (HFR) approach. The effects of configuration interaction and core-polarization have been investigated in detail and the quality of the results has been assessed through a comparison between different HFR physical models. The spectroscopic data listed in the present paper cover electric dipole as well as magnetic dipole and electric quadrupole transitions in a wide range of wavelengths from extreme ultraviolet to near infrared.
      Citation: Atoms
      PubDate: 2017-09-13
      DOI: 10.3390/atoms5030028
      Issue No: Vol. 5, No. 3 (2017)
  • Atoms, Vol. 5, Pages 29: Stark Widths of Na IV Spectral Lines

    • Authors: Milan Dimitrijević, Zoran Simić, Aleksandar Valjarević, Cristina Yubero
      First page: 29
      Abstract: Sodium is a very important element for the research and analysis of astrophysical, laboratory, and technological plasmas, but neither theoretical nor experimental data on Stark broadening of Na IV spectral lines are present in the literature. Using the modified semiempirical method of Dimitrijević and Konjević, here Stark widths have been calculated for nine Na IV transitions. Na IV belongs to the oxygen isoelectronic sequence, and we have calculated Stark widths belonging to singlets, triplets, and quintuplets, as well as with different parent terms. This is used to discuss similarities within one transition array with different multiplicities and parent terms. Additionally, calculated widths will be implemented in the STARK-B database ( which is also a part of the Virtual Atomic and Molecular Data Center (VAMDC—
      Citation: Atoms
      PubDate: 2017-09-18
      DOI: 10.3390/atoms5030029
      Issue No: Vol. 5, No. 3 (2017)
  • Atoms, Vol. 5, Pages 30: Identification and Plasma Diagnostics Study of
           Extreme Ultraviolet Transitions in Highly Charged Yttrium

    • Authors: Roshani Silwal, Endre Takacs, Joan Dreiling, John Gillaspy, Yuri Ralchenko
      First page: 30
      Abstract: Extreme ultraviolet spectra of the L-shell ions of highly charged yttrium (Y 26 + –Y 36 + ) were observed in the electron beam ion trap of the National Institute of Standards and Technology using a flat-field grazing-incidence spectrometer in the wavelength range of 4 nm-20 nm. The electron beam energy was systematically varied from 2.3 keV–6.0 keV to selectively produce different ionization stages. Fifty-nine spectral lines corresponding to Δ n = 0 transitions within the n = 2 and n = 3 shells have been identified using detailed collisional-radiative (CR) modeling of the non-Maxwellian plasma. The uncertainties of the wavelength determinations ranged between 0.0004 nm and 0.0020 nm. Li-like resonance lines, 2s– 2 p 1 / 2 and 2s–2 p 3 / 2 , and the Na-like D lines, 3s– 3 p 1 / 2 and 3s– 3 p 3 / 2 , have been measured and compared with previous measurements and calculations. Forbidden magnetic dipole (M1) transitions were identified and analyzed for their potential applicability in plasma diagnostics using large-scale CR calculations including approximately 1.5 million transitions. Several line ratios were found to show strong dependence on electron density and, hence, may be implemented in the diagnostics of hot plasmas, in particular in fusion devices.
      Citation: Atoms
      PubDate: 2017-09-18
      DOI: 10.3390/atoms5030030
      Issue No: Vol. 5, No. 3 (2017)
  • Atoms, Vol. 5, Pages 31: Radiative and Collisional Molecular Data and
           Virtual Laboratory Astrophysics

    • Authors: Vladimir Srećković, Ljubinko Ignjatović, Darko Jevremović, Veljko Vujčić, Milan Dimitrijević
      First page: 31
      Abstract: Spectroscopy has been crucial for our understanding of physical and chemical phenomena. The interpretation of interstellar line spectra with radiative transfer calculations usually requires two kinds of molecular input data: spectroscopic data (such as energy levels, statistical weights, transition probabilities, etc.) and collision data. This contribution describes how such data are collected, stored, and which limitations exist. Also, here we summarize challenges of atomic/molecular databases and point out our experiences, problems, etc., which we are faced with. We present overview of future developments and needs in the areas of radiative transfer and molecular data.
      Citation: Atoms
      PubDate: 2017-09-19
      DOI: 10.3390/atoms5030031
      Issue No: Vol. 5, No. 3 (2017)
  • Atoms, Vol. 5, Pages 32: Stark Broadening from Impact Theory to

    • Authors: Roland Stamm, Ibtissem Hannachi, Mutia Meireni, Laurence Godbert-Mouret, Mohammed Koubiti, Yannick Marandet, Joël Rosato, Milan Dimitrijević, Zoran Simić
      First page: 32
      Abstract: Impact approximation is widely used for calculating Stark broadening in a plasma. We review its main features and different types of models that make use of it. We discuss recent developments, in particular a quantum approach used for both the emitter and the perturbers. Numerical simulations are a useful tool for gaining insight into the mechanisms at play in impact-broadening conditions. Our simple model allows the integration of the Schrödinger equation for an emitter submitted to a fluctuating electric field. We show how we can approach the impact results, and how we can investigate conditions beyond the impact approximation. The simple concepts developed in impact and simulation approaches enable the analysis of complex problems such as the effect of plasma rogue waves on hydrogen spectra.
      Citation: Atoms
      PubDate: 2017-09-20
      DOI: 10.3390/atoms5030032
      Issue No: Vol. 5, No. 3 (2017)
  • Atoms, Vol. 5, Pages 33: Quasar Black Hole Mass Estimates from
           High-Ionization Lines: Breaking a Taboo'

    • Authors: Paola Marziani, Ascensión Olmo, Mary Martínez-Aldama, Deborah Dultzin, Alenka Negrete, Edi Bon, Natasa Bon, Mauro D’Onofrio
      First page: 33
      Abstract: Can high ionization lines such as CIV λ 1549 provide useful virial broadening estimators for computing the mass of the supermassive black holes that power the quasar phenomenon' The question has been dismissed by several workers as a rhetorical one because blue-shifted, non-virial emission associated with gas outflows is often prominent in CIV λ 1549 line profiles. In this contribution, we first summarize the evidence suggesting that the FWHM of low-ionization lines like H β and MgII λ 2800 provide reliable virial broadening estimators over a broad range of luminosity. We confirm that the line widths of CIV λ 1549 is not immediately offering a virial broadening estimator equivalent to the width of low-ionization lines. However, capitalizing on the results of Coatman et al. (2016) and Sulentic et al. (2017), we suggest a correction to FWHM CIV λ 1549 for Eddington ratio and luminosity effects that, however, remains cumbersome to apply in practice. Intermediate ionization lines (IP ∼ 20–30 eV; AlIII λ 1860 and SiIII] λ 1892) may provide a better virial broadening estimator for high redshift quasars, but larger samples are needed to assess their reliability. Ultimately, they may be associated with the broad-line region radius estimated from the photoionization method introduced by Negrete et al. (2013) to obtain black hole mass estimates independent from scaling laws.
      Citation: Atoms
      PubDate: 2017-09-20
      DOI: 10.3390/atoms5030033
      Issue No: Vol. 5, No. 3 (2017)
  • Atoms, Vol. 5, Pages 15: Shannon Information Entropy in Position Space for
           the Ground and Singly Excited States of Helium with Finite Confinements

    • Authors: Jen-Hao Ou, Yew Ho
      First page: 15
      Abstract: We provide benchmark values for Shannon information entropies in position space for the ground state and ls2s 1Se excited state of helium confined with finite confinement potentials by employing the highly correlated Hylleraas-type wave functions. For the excited state, a “tilt” (small oscillation) on the curve of Shannon entropy as a function of width size for the confinement potential is observed. Justified by the behavior of the electron density, the localization or delocalization of the helium wave functions confined with repulsive and attractive finite oscillator (FO) potentials are examined.
      PubDate: 2017-03-24
      DOI: 10.3390/atoms5020015
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 16: Multiconfiguration Dirac-Hartree-Fock
           Calculations with Spectroscopic Accuracy: Applications to Astrophysics

    • Authors: Per Jönsson, Gediminas Gaigalas, Pavel Rynkun, Laima Radžiūtė, Jörgen Ekman, Stefan Gustafsson, Henrik Hartman, Kai Wang, Michel Godefroid, Charlotte Froese Fischer, Ian Grant, Tomas Brage, Giulio Del Zanna
      First page: 16
      Abstract: Atomic data, such as wavelengths, spectroscopic labels, broadening parameters and transition rates, are necessary for many applications, especially in plasma diagnostics, and for interpreting the spectra of distant astrophysical objects. The experiment with its limited resources is unlikely to ever be able to provide a complete dataset on any atomic system. Instead, the bulk of the data must be calculated. Based on fundamental principles and well-justified approximations, theoretical atomic physics derives and implements algorithms and computational procedures that yield the desired data. We review progress and recent developments in fully-relativistic multiconfiguration Dirac–Hartree–Fock methods and show how large-scale calculations can give transition energies of spectroscopic accuracy, i.e., with an accuracy comparable to the one obtained from observations, as well as transition rates with estimated uncertainties of a few percent for a broad range of ions. Finally, we discuss further developments and challenges.
      PubDate: 2017-04-14
      DOI: 10.3390/atoms5020016
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 17: P-Wave Positron-Hydrogen Scattering,
           Annihilation, and Positronium Formation

    • Authors: Anand Bhatia
      First page: 17
      Abstract: In a previous paper (Bhatia A.K. 2016), a hybrid theory for the scattering of positrons from hydrogen atoms was applied to calculate S-wave phase shifts, annihilation, and positronium formation cross sections. This approach is now being applied to calculate P-wave positron-hydrogen scattering. The present results, obtained using short-range correlation functions along with long-range correlations in the Schrödinger equation at the same time, agree very well with the results obtained in an earlier calculation by Bhatia et al. (1974), using the Feshbach projection operator formalism. In these earlier calculations, the correction due to the long-range correlations was applied to the variational results. In spite of the fact that this ad hoc correction destroyed the variational bound, the final results have been considered accurate. Annihilation cross-sections, positronium formation cross-sections, calculated in the distorted-wave approximation, are also presented.
      PubDate: 2017-04-18
      DOI: 10.3390/atoms5020017
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 18: Elementary Processes and Kinetic Modeling for
           Hydrogen and Helium Plasmas

    • Authors: Roberto Celiberto, Mario Capitelli, Gianpiero Colonna, Giuliano D’Ammando, Fabrizio Esposito, Ratko Janev, Vincenzo Laporta, Annarita Laricchiuta, Lucia Pietanza, Maria Rutigliano, Jogindra Wadehra
      First page: 18
      Abstract: We report cross-sections and rate coefficients for excited states colliding with electrons, heavy particles and walls useful for the description of H 2 /He plasma kinetics under different conditions. In particular, the role of the rotational states in resonant vibrational excitations of the H 2 molecule by electron impact and the calculation of the related cross-sections are illustrated. The theoretical determination of the cross-section for the rovibrational energy exchange and dissociation of H 2 molecule, induced by He atom impact, by using the quasi-classical trajectory method is discussed. Recombination probabilities of H atoms on tungsten and graphite, relevant for the determination of the nascent vibrational distribution, are also presented. An example of a state-to-state plasma kinetic model for the description of shock waves operating in H 2 and He-H 2 mixtures is presented, emphasizing also the role of electronically-excited states in affecting the electron energy distribution function of free electrons. Finally, the thermodynamic properties and the electrical conductivity of non-ideal, high-density hydrogen plasma are finally discussed, in particular focusing on the pressure ionization phenomenon in high-pressure high-temperature plasmas.
      PubDate: 2017-05-02
      DOI: 10.3390/atoms5020018
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 19: Radiative Rates and Electron Impact Excitation
           Rates for Transitions in He II

    • Authors: Kanti Aggarwal, Akinori Igarashi, Francis Keenan, Shinobu Nakazaki
      First page: 19
      Abstract: We report calculations of energy levels, radiative rates, collision strengths and effective collision strengths for transitions among the lowest 25 levels of the n ≤ 5 configurations of He II. The general-purpose relativistic atomic structure package (grasp) and Dirac atomic R-matrix code (darc) are adopted for the calculations. Radiative rates, oscillator strengths and line strengths are reported for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2) and magnetic quadrupole (M2) transitions among the 25 levels. Furthermore, collision strengths and effective collision strengths are listed for all 300 transitions among the above 25 levels over a wide energy (temperature) range up to 9 Ryd (10 5.4 K). Comparisons are made with earlier available results, and the accuracy of the data is assessed.
      PubDate: 2017-05-02
      DOI: 10.3390/atoms5020019
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 20: Configuration Interaction Effects in Unresolved
           5p65dN+1−5p55dN+2+5p65dN5f1 Transition Arrays in Ions Z = 79–92

    • Authors: Luning Liu, Deirdre Kilbane, Padraig Dunne, Xinbing Wang, Gerry O’Sullivan
      First page: 20
      Abstract: Configuration interaction (CI) effects can greatly influence the way in which extreme ultraviolet (EUV) and soft X-ray (SXR) spectra of heavier ions are dominated by emission from unresolved transition arrays (UTAs), the most intense of which originate from Δn = 0, 4p64dN+1−4p54dN+2+4p64dN4f1 transitions. Changing the principle quantum number n, from 4 to 5, changes the origin of the UTA from Δn = 0, 4p64dN+1−4p54dN+2+4p64dN4f1 to Δn = 0, 5p65dN+1−5p55dN+2+5p65dN5f1 transitions. This causes unexpected and significant changes in the impact of configuration interaction from that observed in the heavily studied n = 4 – n = 4 arrays. In this study, the properties of n = 5 – n = 5 arrays have been investigated theoretically with the aid of Hartree-Fock with configuration interaction (HFCI) calculations. In addition to predicting the wavelengths and spectral details of the anticipated features, the calculations show that the effects of configuration interaction are quite different for the two different families of Δn = 0 transitions, a conclusion which is reinforced by comparison with experimental results.
      PubDate: 2017-05-21
      DOI: 10.3390/atoms5020020
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 21: Inter-Series Interactions on the Atomic
           Photoionization Spectra Studied by the Phase-Shifted Multichannel-Quantum
           Defect Theory

    • Authors: Chun-Woo Lee
      First page: 21
      Abstract: Development in mathematical formulations of parameterizing the resonance structures using the phase-shifted multichannel quantum defect theory (MQDT) and their use in analyzing the effect of inter-series interactions on the autoionizing Rydberg spectra is reviewed. Reformulation of the short-range scattering matrix into the form analogous to S = SBSR in scattering theory are the crucial step in this development. Formulation adopts different directions and goals depending on whether autoionizing series converge to the same limit (degenerate) or to different limits (nondegenerate) because of the different nature of the perturbation. For the nondegenerate case, finding the simplest form of profile index functions of the autoionizing spectra with the minimal number of parameters is the main goal and some results are reviewed. For the degenerate case where perturbation acts uniformly throughout the entire series, isolation of the overlapped autoionizing series into the unperturbed autoionizing series is the key objective in research and some results in that direction are reviewed.
      PubDate: 2017-05-20
      DOI: 10.3390/atoms5020021
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 22: Detailed Opacity Calculations for Astrophysical

    • Authors: Jean-Christophe Pain, Franck Gilleron, Maxime Comet
      First page: 22
      Abstract: Nowadays, several opacity codes are able to provide data for stellar structure models, but the computed opacities may show significant differences. In this work, we present state-of-the-art precise spectral opacity calculations, illustrated by stellar applications. The essential role of laboratory experiments to check the quality of the computed data is underlined. We review some X-ray and XUV laser and Z-pinch photo-absorption measurements as well as X-ray emission spectroscopy experiments involving hot dense plasmas produced by ultra-high-intensity laser irradiation. The measured spectra are systematically compared with the fine-structure opacity code SCO-RCG. The focus is on iron, due to its crucial role in understanding asteroseismic observations of β Cephei-type and Slowly Pulsating B stars, as well as of the Sun. For instance, in β Cephei-type stars, the iron-group opacity peak excites acoustic modes through the “kappa-mechanism”. Particular attention is paid to the higher-than-predicted iron opacity measured at the Sandia Z-machine at solar interior conditions. We discuss some theoretical aspects such as density effects, photo-ionization, autoionization or the “filling-the-gap” effect of highly excited states.
      PubDate: 2017-05-30
      DOI: 10.3390/atoms5020022
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 23: The Third Spectrum of Indium: In III

    • Authors: Swapnil, Tauheed Ahmad
      First page: 23
      Abstract: The present investigation reports on the extended study of the third spectrum of indium (In III). This spectrum was previously analyzed in many articles, but, nevertheless, this study represents a significant extension of the previous analyses. The main new contribution is connected to the observation of transitions involving core-excited configurations. Previous data are critically evaluated and in some cases are corrected. The spectra were recorded on 3-m as well as on 10.7-m normal incidence spectrographs using a triggered spark source. Theoretical calculations were made with Cowan’s code. The analysis results in the identifications of 70 spectral lines and determination of 24 new energy levels. In addition, the manuscript represents a compilation of all presently available data on In III.
      PubDate: 2017-06-13
      DOI: 10.3390/atoms5020023
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 1: Acknowledgement to Reviewers of Atoms in 2016

    • Authors: Atoms Editorial Office
      First page: 1
      Abstract: The editors of Atoms would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2016.[...]
      PubDate: 2017-01-10
      DOI: 10.3390/atoms5010001
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 2: An Investigation on the He−(1s2s2 2S)
           Resonance in Debye Plasmas

    • Authors: Arijit Ghoshal, Yew Ho
      First page: 2
      Abstract: The effect of Debye plasma on the 1 s 2 s 2 2 S resonance states in the scattering of electron from helium atom has been investigated within the framework of the stabilization method. The interactions among the charged particles in Debye plasma have been modelled by Debye–Huckel potential. The 1 s 2 s excited state of the helium atom has been treated as consisting of a H e + ionic core plus an electron moving around. The interaction between the core and the electron has then been modelled by a model potential. It has been found that the background plasma environment significantly affects the resonance states. To the best of our knowledge, such an investigation of 1 s 2 s 2 2 S resonance states of the electron–helium system embedded in Debye plasma environment is the first reported in the literature.
      PubDate: 2017-01-11
      DOI: 10.3390/atoms5010002
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 3: Combining Multiconfiguration and Perturbation
           Methods: Perturbative Estimates of Core–Core Electron Correlation
           Contributions to Excitation Energies in Mg-Like Iron

    • Authors: Stefan Gustafsson, Per Jönsson, Charlotte Froese Fischer, Ian Grant
      First page: 3
      Abstract: Large configuration interaction (CI) calculations can be performed if part of the interaction is treated perturbatively. To evaluate the combined CI and perturbative method, we compute excitation energies for the 3 l 3 l ′ , 3 l 4 l ′ and 3 s 5 l states in Mg-like iron. Starting from a CI calculation including valence and core–valence correlation effects, it is found that the perturbative inclusion of core–core electron correlation halves the mean relative differences between calculated and observed excitation energies. The effect of the core–core electron correlation is largest for the more excited states. The final relative differences between calculated and observed excitation energies is 0.023%, which is small enough for the calculated energies to be of direct use in line identifications in astrophysical and laboratory spectra.
      PubDate: 2017-01-12
      DOI: 10.3390/atoms5010003
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 4: High-Precision Measurements of the Bound
           Electron’s Magnetic Moment

    • Authors: Sven Sturm, Manuel Vogel, Florian Köhler-Langes, Wolfgang Quint, Klaus Blaum, Günter Werth
      First page: 4
      Abstract: Highly charged ions represent environments that allow to study precisely one or more bound electrons subjected to unsurpassed electromagnetic fields. Under such conditions, the magnetic moment (g-factor) of a bound electron changes significantly, to a large extent due to contributions from quantum electrodynamics. We present three Penning-trap experiments, which allow to measure magnetic moments with ppb precision and better, serving as stringent tests of corresponding calculations, and also yielding access to fundamental quantities like the fine structure constant α and the atomic mass of the electron. Additionally, the bound electrons can be used as sensitive probes for properties of the ionic nuclei. We summarize the measurements performed so far, discuss their significance, and give a detailed account of the experimental setups, procedures and the foreseen measurements.
      PubDate: 2017-01-21
      DOI: 10.3390/atoms5010004
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 5: Hyperfine Structure and Isotope Shifts in Dy II

    • Authors: Dylan Del Papa, Richard Holt, S. Rosner
      First page: 5
      Abstract: Using fast-ion-beam laser-fluorescence spectroscopy (FIBLAS), we have measured the hyperfine structure (hfs) of 14 levels and an additional four transitions in Dy II and the isotope shifts (IS) of 12 transitions in the wavelength range of 422–460 nm. These are the first precision measurements of this kind in Dy II. Along with hfs and IS, new undocumented transitions were discovered within 3 GHz of the targeted transitions. These atomic data are essential for astrophysical studies of chemical abundances, allowing correction for saturation and the effects of blended lines. Lanthanide abundances are important in diffusion modeling of stellar interiors, and in the mechanisms and history of nucleosynthesis in the universe. Hfs and IS also play an important role in the classification of energy levels, and provide a benchmark for theoretical atomic structure calculations.
      PubDate: 2017-01-20
      DOI: 10.3390/atoms5010005
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 6: JJ2LSJ Transformation and Unique Labeling for
           Energy Levels

    • Authors: Gediminas Gaigalas, Charlotte Fischer, Pavel Rynkun, Per Jönsson
      First page: 6
      Abstract: The JJ2LSJ program, which is important not only for the GRASP2K package but for the atom theory in general, is presented. The program performs the transformation of atomic state functions(ASFs) from a jj-coupled CSF basis into an LSJ-coupled CSF basis. In addition, the program implements a procedure that assigns a unique label to all energy levels. Examples of how to use the JJ2LSJ program are given. Several cases are presented where there is a unique labeling problem.
      PubDate: 2017-01-27
      DOI: 10.3390/atoms5010006
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 7: Core Effects on Transition Energies for 3dk
           Configurations in Tungsten Ions

    • Authors: Charlotte Fischer, Gediminas Gaigalas, Per Jönsson
      First page: 7
      Abstract: Allenergylevelsofthe3dk,k=1,2,...,8,9,configurationsfortungstenions,computedusing the GRASP2K fully relativistic code based on the variational multiconfiguration Dirac–Hartree–Fock method, are reported. Included in the calculations are valence correlation where all 3s,3p,3d orbitals are considered to be valence orbitals, as well as core–valence and core–core effects from the 2s,2p subshells. Results are compared with other recent theory and with levels obtained from the wavelengths of lines observed in the experimental spectra. It is shown that the core correlation effects considerably reduce the disagreement with levels linked directly to observed wavelengths, but may differ significantly from the NIST levels, where an unknown shift of the levels could not be determined from experimental wavelengths. For low values of k, levels were in good agreement with relativistic many-body perturbation levels, but for 2 < k < 8, the present results were in better agreement with observation.
      PubDate: 2017-02-08
      DOI: 10.3390/atoms5010007
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 8: Calculation of Rates of 4p–4d Transitions in
           Ar II

    • Authors: Alan Hibbert
      First page: 8
      Abstract: Recent experimental work by Belmonte et al. (2014) has given rates for some 4p–4d transitions that are significantly at variance with the previous experimental work of Rudko and Tang (1967) recommended in the NIST tabulations. To date, there are no theoretical rates with which to compare. In this work, we provide such theoretical data. We have undertaken a substantial and systematic configuration interaction calculation, with an extrapolation process applied to ab initio mixing coefficients, which gives energy differences in agreement with experiment. The length and velocity forms give values that are within 10%–15% of each other. Our results are in sufficiently close agreement with those of Belmonte et al. that we can confidently recommend that their results are much more accurate than the early results of Rudko and Tang, and should be adopted in place of the latter.
      PubDate: 2017-02-21
      DOI: 10.3390/atoms5010008
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 9: The Cu II Spectrum

    • Authors: Alexander Kramida, Gillian Nave, Joseph Reader
      First page: 9
      Abstract: New wavelength measurements in the vacuum ultraviolet (VUV), ultraviolet and visible spectral regions have been combined with available literature data to refine and extend the description of the spectrum of singly ionized copper (Cu II). In the VUV region, we measured 401 lines using a concave grating spectrograph and photographic plates. In the UV and visible regions, we measured 276 lines using a Fourier-transform spectrometer. These new measurements were combined with previously unpublished data from the thesis of Ross, with accurate VUV grating measurements of Kaufman and Ward, and with less accurate older measurements of Shenstone to construct a comprehensive list of ≈2440 observed lines, from which we derived a revised set of 379 optimized energy levels, complemented with 89 additional levels obtained using series formulas. Among the 379 experimental levels, 29 are new. Intensities of all lines observed in different experiments have been reduced to the same uniform scale by using newly calculated transition probabilities (A-values). We combined our calculations with published measured and calculated A-values to provide a set of 555 critically evaluated transition probabilities with estimated uncertainties, 162 of which are less than 20%.
      PubDate: 2017-02-24
      DOI: 10.3390/atoms5010009
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 10: The Role of the Hyperfine Structure for the
           Determination of Improved Level Energies of Ta II, Pr II and La II

    • Authors: Laurentius Windholz
      First page: 10
      Abstract: For the determination of improved energy levels of ionic spectra of elements with large values of nuclear magnetic dipole moment (and eventually large values of nuclear quadrupole moments), it is necessary to determine the center of gravity of spectral lines from resolved hyperfine structure patterns appearing in highly resolved spectra. This is demonstrated on spectral lines of Ta II, Pr II and La II. Blend situations (different transitions with accidentally nearly the same wave number difference between the combining levels) must also be considered.
      PubDate: 2017-02-28
      DOI: 10.3390/atoms5010010
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 11: Resonance Transitions in the Spectra of the
           Ag6+–Ag8+ Ions

    • Authors: Alexander Ryabtsev, Edward Kononov
      First page: 11
      Abstract: The spectrum of silver, excited in a vacuum spark, was recorded in the region 150–350 Å on a 3-m grazing incidence spectrograph. The resonance 4dk–(4dk−15p + 4dk−14f + 4p54dk+1) was studied in the Ag6+–Ag8+ spectra (Ag VII–Ag IX) with k = 5–3, respectively. Several hundred lines were identified with the aid of the Cowan code and orthogonal operator technique calculations. The energy levels were found and the transition probabilities were calculated.
      PubDate: 2017-03-04
      DOI: 10.3390/atoms5010011
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 12: Spectral Analysis of Moderately Charged Rare-Gas

    • Authors: Jorge Reyna Almandos, Mónica Raineri
      First page: 12
      Abstract: This article presents a review concerning the spectral analysis of several ions of neon, argon, krypton and xenon, with impact on laser studies and astrophysics that were mainly carried out in our collaborative groups between Argentina and Brazil during many years. The spectra were recorded from the vacuum ultraviolet to infrared regions using pulsed discharges. Semi-empirical approaches with relativistic Hartree–Fock and Dirac-Fock calculations were also included in these investigations. The spectral analysis produced new classified lines and energy levels. Lifetimes and oscillator strengths were also calculated.
      PubDate: 2017-03-07
      DOI: 10.3390/atoms5010012
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 13: Direct Observation of the M1 Transition between
           the Ground Term Fine Structure Levels of W VIII

    • Authors: Momoe Mita, Hiroyuki Sakaue, Daiji Kato, Izumi Murakami, Nobuyuki Nakamura
      First page: 13
      Abstract: We present a direct observation of the M1 transition between the fine structure splitting in the 4 f 13 5 s 2 5 p 6 2 F ground term of W VIII. The spectroscopic data of few-times ionized tungsten ions are important for the future ITER diagnostics, but there is a serious lack of data. The present study is part of an ongoing effort to solve this problem. Emission from the tungsten ions produced and trapped in a compact electron beam ion trap is observed with a Czerny–Turner visible spectrometer. Spectra in the EUV range are also observed at the same time to help identify the previously-unreported visible lines. The observed wavelength 574.47 ± 0.03 nm (air), which corresponds to the fine structure splitting of 17,402.5 ± 0.9 cm − 1 , shows reasonable agreement with the previously reported value 17,410 ± 5 cm − 1 obtained indirectly through the analysis of EUV spectra [Ryabtsev et al., Atoms 3 (2015) 273].
      PubDate: 2017-03-08
      DOI: 10.3390/atoms5010013
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 14: Electroweak Decay Studies of Highly Charged
           Radioactive Ions with TITAN at TRIUMF

    • Authors: Kyle Leach, Iris Dillmann, Renee Klawitter, Erich Leistenschneider, Annika Lennarz, Thomas Brunner, Dieter Frekers, Corina Andreoiu, Anna Kwiatkowski, Jens Dilling
      First page: 14
      Abstract: Several modes of electroweak radioactive decay require an interaction between the nucleus and bound electrons within the constituent atom. Thus, the probabilities of the respective decays are not only influenced by the structure of the initial and final states in the nucleus, but can also depend strongly on the atomic charge. Conditions suitable for the partial or complete ionization of these rare isotopes occur naturally in hot, dense astrophysical environments, but can also be artificially generated in the laboratory to selectively block certain radioactive decay modes. Direct experimental studies on such scenarios are extremely difficult due to the laboratory conditions required to generate and store radioactive ions at high charge states. A new electron-beam ion trap (EBIT) decay setup with the TITAN experiment at TRIUMF has successfully demonstrated such techniques for performing spectroscopy on the radioactive decay of highly charged ions.
      PubDate: 2017-03-21
      DOI: 10.3390/atoms5010014
      Issue No: Vol. 5, No. 1 (2017)
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