Atoms

1368 KiB

Open AccessArticle

by Swapnil and Tauheed Ahmad

Atoms 2017, 5(2), 23; https://doi.org/10.3390/atoms5020023 - 13 Jun 2017

Viewed by 3559

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Spectra of Ionized Atoms: From Laboratory to Space)

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4718 KiB

Open AccessFeature PaperArticle

Detailed Opacity Calculations for Astrophysical Applications

by Jean-Christophe Pain, Franck Gilleron and Maxime Comet

Atoms 2017, 5(2), 22; https://doi.org/10.3390/atoms5020022 - 30 May 2017

Cited by 12 | Viewed by 5309

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Atomic and Molecular Opacity Data for Astrophysics)

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3801 KiB

Open AccessFeature PaperArticle

Configuration Interaction Effects in Unresolved 5p⁶5d^N+1−5p⁵5d^N+2+5p⁶5d^N5f¹ Transition Arrays in Ions Z = 79–92

by Luning Liu, Deirdre Kilbane, Padraig Dunne, Xinbing Wang and Gerry O’Sullivan

Atoms 2017, 5(2), 20; https://doi.org/10.3390/atoms5020020 - 21 May 2017

Cited by 3 | Viewed by 4436

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, 4p⁶ [...] Read more.

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, 4p⁶4d^N+1−4p⁵4d^N+2+4p⁶4d^N4f¹ transitions. Changing the principle quantum number n, from 4 to 5, changes the origin of the UTA from Δn = 0, 4p⁶4d^N+1−4p⁵4d^N+2+4p⁶4d^N4f¹ to Δn = 0, 5p⁶5d^N+1−5p⁵5d^N+2+5p⁶5d^N5f¹ 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. Full article

(This article belongs to the Special Issue Spectra of Ionized Atoms: From Laboratory to Space)

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4289 KiB

Open AccessReview

Inter-Series Interactions on the Atomic Photoionization Spectra Studied by the Phase-Shifted Multichannel-Quantum Defect Theory

by Chun-Woo Lee

Atoms 2017, 5(2), 21; https://doi.org/10.3390/atoms5020021 - 20 May 2017

Cited by 1 | Viewed by 3324

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 [...] Read more.

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 = S_BS_R 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. Full article

(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)

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556 KiB

Open AccessFeature PaperArticle

Radiative Rates and Electron Impact Excitation Rates for Transitions in He II

by Kanti M. Aggarwal, Akinori Igarashi, Francis P. Keenan and Shinobu Nakazaki

Atoms 2017, 5(2), 19; https://doi.org/10.3390/atoms5020019 - 02 May 2017

Cited by 4 | Viewed by 3770

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 \leq

5 configurations of He II. The general-purpose relativistic atomic structure package (grasp) and Dirac atomic R-matrix [...] Read more.

We report calculations of energy levels, radiative rates, collision strengths and effective collision strengths for transitions among the lowest 25 levels of the

n \leq

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. Full article

(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)

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874 KiB

Open AccessFeature PaperArticle

Elementary Processes and Kinetic Modeling for Hydrogen and Helium Plasmas

by Roberto Celiberto, Mario Capitelli, Gianpiero Colonna, Giuliano D’Ammando, Fabrizio Esposito, Ratko K. Janev, Vincenzo Laporta, Annarita Laricchiuta, Lucia Daniela Pietanza, Maria Rutigliano and Jogindra M. Wadehra

Atoms 2017, 5(2), 18; https://doi.org/10.3390/atoms5020018 - 02 May 2017

Cited by 13 | Viewed by 5468

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Atomic and Molecular Data for Hydrogen and Helium in Fusion Plasma)

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244 KiB

Open AccessFeature PaperArticle

P-Wave Positron-Hydrogen Scattering, Annihilation, and Positronium Formation

by Anand K. Bhatia

Atoms 2017, 5(2), 17; https://doi.org/10.3390/atoms5020017 - 18 Apr 2017

Cited by 5 | Viewed by 2945

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 [...] Read more.

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. Full article

(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)

353 KiB

Open AccessFeature PaperReview

Multiconfiguration Dirac-Hartree-Fock Calculations with Spectroscopic Accuracy: Applications to Astrophysics

by 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 and Giulio Del Zanna

Atoms 2017, 5(2), 16; https://doi.org/10.3390/atoms5020016 - 14 Apr 2017

Cited by 43 | Viewed by 6459

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Spectra of Ionized Atoms: From Laboratory to Space)

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6398 KiB

Open AccessArticle

Shannon Information Entropy in Position Space for the Ground and Singly Excited States of Helium with Finite Confinements

by Jen-Hao Ou and Yew Kam Ho

Atoms 2017, 5(2), 15; https://doi.org/10.3390/atoms5020015 - 24 Mar 2017

Cited by 23 | Viewed by 5063

Abstract

We provide benchmark values for Shannon information entropies in position space for the ground state and ls2s ¹S^e excited state of helium confined with finite confinement potentials by employing the highly correlated Hylleraas-type wave functions. For the excited state, a “tilt” [...] Read more.

We provide benchmark values for Shannon information entropies in position space for the ground state and ls2s ¹S^e 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. Full article

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Atoms, Volume 5, Issue 2 (June 2017) – 9 articles

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