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Atoms, Volume 7, Issue 3 (September 2019)

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Open AccessArticle
Positron Impact Excitation of the 2S State of Atomic Hydrogen
Received: 17 May 2019 / Revised: 6 July 2019 / Accepted: 6 July 2019 / Published: 10 July 2019
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Abstract
The excitation cross-sections of the 2S state of atomic hydrogen at low (near threshold energy) to high incident positron energies (10.30 to 300 eV) have been calculated using the variational polarized-orbital method. Nine partial waves have been used to obtain converged cross-sections [...] Read more.
The excitation cross-sections of the 2S state of atomic hydrogen at low (near threshold energy) to high incident positron energies (10.30 to 300 eV) have been calculated using the variational polarized-orbital method. Nine partial waves have been used to obtain converged cross-sections in the above energy range. The cross sections compared to the electron-impact excitation of the S state of atomic hydrogen are larger in the present case. The maximum cross section is 3.63(−1) π a 0 2 at 16.5 eV compared to 1.37(−1) π a 0 2 at 11.14 eV for the electron-impact excitation. The present results are compared with other calculations. Cross-sections have also been calculated in the Born approximation in which the polarization of the target has been included. Differential cross sections were calculated at k = 1.0 (13.6eV), 2.5 (85 eV), 3.483 (200 3V), and 4.696 (300 eV). Full article
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Open AccessErratum
Erratum: Oks, E. Review of Recent Advances in the Analytical Theory of Stark Broadening of Hydrogenic Spectral Lines in Plasmas: Applications to Laboratory Discharges and Astrophysical Objects. Atoms 2018, 6, 50
Received: 2 July 2019 / Revised: 2 July 2019 / Accepted: 2 July 2019 / Published: 5 July 2019
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Abstract
The author wishes to make the following corrections to this paper [...] Full article
(This article belongs to the Special Issue Stark Broadening of Spectral Lines in Plasmas) Printed Edition available
Open AccessArticle
Cross Sections and Rate Coefficients for Rovibrational Excitation of HeH+ Isotopologues by Electron Impact
Received: 29 May 2019 / Revised: 21 June 2019 / Accepted: 28 June 2019 / Published: 5 July 2019
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Abstract
Cross sections and thermal rate coefficients for rotational and vibration excitation of the four stable isotopologues of the 4HeH+ ion by electron impact are presented. The data are calculated using a previously developed theoretical approach. The obtained rate coefficients are fitted [...] Read more.
Cross sections and thermal rate coefficients for rotational and vibration excitation of the four stable isotopologues of the 4 HeH + ion by electron impact are presented. The data are calculated using a previously developed theoretical approach. The obtained rate coefficients are fitted to analytical formulas with the 10–10,000 K interval of applicability. These present results could be useful in tokamak plasma and astrophysical modeling and can help in the detection of these species in the interstellar medium. Full article
(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)
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Open AccessArticle
Soft X-Ray Spectroscopy of Rare-Earth Elements in LHD Plasmas
Received: 31 May 2019 / Revised: 28 June 2019 / Accepted: 30 June 2019 / Published: 3 July 2019
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Abstract
Soft X-ray spectra from high Z rare-earth (lanthanide) elements have been systematically observed in optically thin, high-temperature plasmas produced in the Large Helical Device (LHD), a facility for magnetically confined fusion research. It has been demonstrated that the discrete and quasicontinuum (UTA) spectral [...] Read more.
Soft X-ray spectra from high Z rare-earth (lanthanide) elements have been systematically observed in optically thin, high-temperature plasmas produced in the Large Helical Device (LHD), a facility for magnetically confined fusion research. It has been demonstrated that the discrete and quasicontinuum (UTA) spectral features from highly charged lanthanide ions are observed depending on the plasma temperature. The analyses of the measured spectra are ongoing by comparisons with theoretical calculations and/or previous experimental data available. The discrete spectra recorded in high-temperature conditions are dominated by individual lines of Ge- to Ni-like ions, while prominent peaks in the narrowed UTA spectra observed in low-temperature conditions are well explained by the transitions of Ag- to Rh-like ions. Full article
(This article belongs to the Special Issue Atomic Processes in Plasmas: APiP-2019)
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Open AccessArticle
Geometric Phase Effects in Ultracold Chemical Reactions
Received: 9 April 2019 / Revised: 17 June 2019 / Accepted: 27 June 2019 / Published: 3 July 2019
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Abstract
The role of the geometric phase effect in chemical reaction dynamics has long been a topic of active experimental and theoretical investigations. The topic has received renewed interest in recent years in cold and ultracold chemistry where it was shown to play a [...] Read more.
The role of the geometric phase effect in chemical reaction dynamics has long been a topic of active experimental and theoretical investigations. The topic has received renewed interest in recent years in cold and ultracold chemistry where it was shown to play a decisive role in state-to-state chemical dynamics. We provide a brief review of these developments focusing on recent studies of O + OH and hydrogen exchange in the H + H 2 and D + HD reactions at cold and ultracold temperatures. Non-adiabatic effects in ultracold chemical dynamics arising from the conical intersection between two electronic potential energy surfaces are also briefly discussed. By taking the hydrogen exchange reaction as an illustrative example it is shown that the inclusion of the geometric phase effect captures the essential features of non-adiabatic dynamics at collision energies below the conical intersection. Full article
(This article belongs to the Special Issue Few-body Physics in Ultracold Quantum Gases)
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Open AccessArticle
Cowan Code: 50 Years of Growing Impact on Atomic Physics
Received: 28 May 2019 / Revised: 17 June 2019 / Accepted: 19 June 2019 / Published: 2 July 2019
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Abstract
The famous Cowan’s book, “The Theory of Atomic Structure and Spectra”, published in 1981, and his suite of computer codes based on it, continue to be highly influential in atomic physics and many other research areas. As of September 2018, there have been [...] Read more.
The famous Cowan’s book, “The Theory of Atomic Structure and Spectra”, published in 1981, and his suite of computer codes based on it, continue to be highly influential in atomic physics and many other research areas. As of September 2018, there have been more than 5000 citations to Cowan’s book and codes, and each year adds about 150 citations to this list. The present work briefly describes what these codes do and why they are responsible for most of the current progress in the analyses of atomic spectra. Various modifications of these codes, including my own, will also be described. Full article
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Open AccessArticle
Laser-Plasma and Self-Absorption Measurements with Applications to Analysis of Atomic and Molecular Stellar Astrophysics Spectra
Received: 28 May 2019 / Revised: 20 June 2019 / Accepted: 26 June 2019 / Published: 1 July 2019
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Abstract
This work discusses laboratory measurements of atomic and diatomic molecular species in laser-plasma generated in gases. Noticeable self-absorption of the Balmer series hydrogen alpha line occurs for electron densities of the order of one tenth of standard ambient temperature and pressure density. Emission [...] Read more.
This work discusses laboratory measurements of atomic and diatomic molecular species in laser-plasma generated in gases. Noticeable self-absorption of the Balmer series hydrogen alpha line occurs for electron densities of the order of one tenth of standard ambient temperature and pressure density. Emission spectra of selected diatomic molecules in air or specific gaseous mixtures at or near atmospheric pressure reveal minimal plasma re-absorption. Abel inversion of the plasma in selected gases and gas mixtures confirm expansion dynamics that unravel regions of atomic and molecular species of different electron temperature and density. Time resolved spectroscopy diagnoses self-absorption of hydrogen alpha and hydrogen beta lines in ultra-high pure hydrogen gas. Radiation from a Nd:YAG laser device induces micro-plasma for pulse widths in the range of 6–14 ns, energies in the range of 100–800 mJ, and peak irradiances of the order 1–10 TW/cm 2 . Atomic line profiles yield electron density and temperature from fitting of line profiles to wavelength and sensitivity corrected spectral radiance data. Analysis of measured diatomic emission data yields excitation temperature of primarily molecular recombination spectra. Applications of the laboratory experiments extend to investigations of stellar astrophysics white dwarf spectra. Full article
(This article belongs to the Special Issue Atomic Processes in Plasmas: APiP-2019)
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Open AccessArticle
Towards the Search for Thallium Nuclear Schiff Moment in Polyatomic Molecules: Molecular Properties of Thallium Monocyanide (TlCN)
Received: 29 April 2019 / Revised: 19 June 2019 / Accepted: 25 June 2019 / Published: 29 June 2019
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Abstract
Molecular properties of the thallium monocyanide (Tl·CN) system in its ground electronic state are studied using high-precision ab initio relativistic two-component pseudopotential replacing 60 inner-core electrons of Tl. A relativistic coupled-cluster method with single, double and perturbative triple amplitudes is employed to account [...] Read more.
Molecular properties of the thallium monocyanide (Tl·CN) system in its ground electronic state are studied using high-precision ab initio relativistic two-component pseudopotential replacing 60 inner-core electrons of Tl. A relativistic coupled-cluster method with single, double and perturbative triple amplitudes is employed to account for electronic correlations. Extrapolation of results to the complete basis set limit is used for all studied properties. The global potential energy minimum of Tl·CN corresponds to the linear cyanide (TlCN) isomer, while the non-rigid isocyanide-like (TlNC) structure lies by approximately 11 kJ/mol higher in energy. The procedure of restoration of the wavefunction in the “core” region of Tl atom was applied to calculate the interaction of the Tl nuclear Schiff moment with electrons. The parameter X of the interaction of the Tl nuclear Schiff moment with electrons in the linear TlCN molecule equals 7150 a.u. The prospects of using the TlCN molecule for the experimental detection of the nuclear Schiff moment are discussed. Full article
(This article belongs to the Special Issue Search for New Physics with Cold and Controlled Molecules)
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Open AccessArticle
Measurements of Gaseous Hydrogen–Nitrogen Laser-Plasma
Received: 14 June 2019 / Revised: 26 June 2019 / Accepted: 26 June 2019 / Published: 29 June 2019
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Abstract
This work communicates laser-plasma experiments in a gaseous mixture of hydrogen and nitrogen. Time-resolved spectroscopy measures the first four Balmer-series hydrogen lines together with selected neutral and ionized nitrogen lines. Optical breakdown plasma is generated in a 1:1 hydrogen:nitrogen mixture at ambient temperature [...] Read more.
This work communicates laser-plasma experiments in a gaseous mixture of hydrogen and nitrogen. Time-resolved spectroscopy measures the first four Balmer-series hydrogen lines together with selected neutral and ionized nitrogen lines. Optical breakdown plasma is generated in a 1:1 hydrogen:nitrogen mixture at ambient temperature and 0.27-atm pressure. Time-resolved spectroscopy records emitted radiation with spatial resolution along the slit height for the H α , H β , H γ , and H δ lines. For 13 selected time delays from 0.25 μ s to 3.25 μ s and 0.025 μ s gate-widths, micro-plasma diagnostics is evaluated. Of interest are the peak separation and width of H δ and width of H γ for electron densities in the range of 0.1 to 1.0 × 10 17 cm 3 , and comparisons with H β and H α diagnostics. Integral inversions interrogate spatial distributions of the plasma expansion. Applications include laboratory and stellar astrophysics plasma diagnosis. Full article
(This article belongs to the Special Issue Laser Plasma Spectroscopy Applications)
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Open AccessArticle
The Electron Impact Ionization Cross Sections of Methanol, Ethanol and 1-Propanol
Received: 19 May 2019 / Revised: 7 June 2019 / Accepted: 9 June 2019 / Published: 26 June 2019
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Abstract
In the present investigation, the plane-wave Born approximation was employed to calculate the total ionization cross sections by electron impact of methanol, ethanol and 1-propanol from the threshold of ionization to 10 MeV. This method requires continuum generalized oscillator strengths (CGOSs). The two [...] Read more.
In the present investigation, the plane-wave Born approximation was employed to calculate the total ionization cross sections by electron impact of methanol, ethanol and 1-propanol from the threshold of ionization to 10 MeV. This method requires continuum generalized oscillator strengths (CGOSs). The two different semi-phenomenological expressions of CGOS, given by Mayol and Salvat and Weizsacker and Williams, along with approximated form of the continuum optical oscillator strength (COOS) by Khare et al. were used. Furthermore, the average of the above two CGOSs was also used. The calculated ionization cross sections were compared to the available previous theoretical results and experimental data. Out of three CGOSs, the present results with the average CGOS were found in good agreement with the available experimental results for all the considered molecules. Collision parameters CRP were also calculated from 0.1 to 100 MeV and the calculations were found to be in excellent agreement with the experimental results of Reike and Prepejchal. Full article
(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)
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