Research

Jump to: Review

20 pages, 4477 KiB

Open AccessArticle

L-Shell Photoionization of Magnesium-like Ions with New Results for Cl⁵⁺

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and

Atoms 2023, 11(4), 66; https://doi.org/10.3390/atoms11040066 - 03 Apr 2023

Viewed by 1115

Abstract

This study reports on the absolute photoionization cross sections for the magnesium-like Cl⁵⁺ ion over the 190–370 eV photon energy range, corresponding to the L-shell (2s and 2p subshells) excitation regime. The experiments were performed using the Multi-Analysis Ion Apparatus (MAIA) on [...] Read more.

This study reports on the absolute photoionization cross sections for the magnesium-like Cl⁵⁺ ion over the 190–370 eV photon energy range, corresponding to the L-shell (2s and 2p subshells) excitation regime. The experiments were performed using the Multi-Analysis Ion Apparatus (MAIA) on the PLéIADES beamline at the SOLEIL synchrotron radiation storage ring facility. Single and double ionization ion yields, produced by photoionization of the 2p subshell of the Cl⁵⁺ ion from the 2p⁶3s^2 1S₀ ground state and the 2p⁶3s3p ³P_0,1,2 metastable levels, were observed, as well as 2s excitations. Theoretical calculations of the photoionization cross sections using the Multi-Configuration Dirac-Fock and R-matrix approaches were carried out, and the results were compared with the experimental data. The Cl⁵⁺ results were examined within the overall evolution of L-shell excitation for the early members of the Mg-like isoelectronic sequence (Mg, Al⁺, Si²⁺, S⁴⁺, Cl⁵⁺). Characteristic photon energies for P³⁺ were estimated by interpolation. Full article

(This article belongs to the Special Issue Photoionization of Atoms)

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14 pages, 902 KiB

Open AccessEditor’s ChoiceArticle

The Shapes of Stellar Spectra

by

Carlos Allende Prieto

Atoms 2023, 11(3), 61; https://doi.org/10.3390/atoms11030061 - 20 Mar 2023

Cited by 3 | Viewed by 971

Abstract

Stellar atmospheres separate the hot and dense stellar interiors from the emptiness of space. Radiation escapes from the outermost layers of a star, carrying direct physical information. Underneath the atmosphere, the very high opacity keeps radiation thermalized and resembling a black body with [...] Read more.

Stellar atmospheres separate the hot and dense stellar interiors from the emptiness of space. Radiation escapes from the outermost layers of a star, carrying direct physical information. Underneath the atmosphere, the very high opacity keeps radiation thermalized and resembling a black body with the local temperature. In the atmosphere the opacity drops, and radiative energy leaks out, which is redistributed in wavelength according to the physical processes by which matter and radiation interact, in particular photoionization. In this article, I will evaluate the role of photoionization in shaping the stellar energy distribution of stars. To that end, I employ simple, state-of-the-art plane-parallel model atmospheres and a spectral synthesis code, dissecting the effects of photoionization from different chemical elements and species, for stars of different masses in the range of 0.3 to 2 M

_{⊙}

. I examine and interpret the changes in the observed spectral energy distributions of the stars as a function of the atmospheric parameters. The photoionization of atomic hydrogen and H

^{-}

are the most relevant contributors to the continuum opacity in the optical and near-infrared regions, while heavier elements become important in the ultraviolet region. In the spectra of the coolest stars (spectral types M and later), the continuum shape from photoionization is no longer recognizable due to the accumulation of lines, mainly from molecules. These facts have been known for a long time, but the calculations presented provide an updated quantitative evaluation and insight into the role of photoionization on the structure of stellar atmospheres. Full article

(This article belongs to the Special Issue Photoionization of Atoms)

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13 pages, 972 KiB

Open AccessArticle

Experimental and Theoretical Study of Photoionization of Cl III

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,

,

,

Alejandro Morales-Mori

,

Dag Hanstorp

,

Antonio M. Juárez

and

Guillermo Hinojosa

Atoms 2023, 11(2), 28; https://doi.org/10.3390/atoms11020028 - 03 Feb 2023

Cited by 1 | Viewed by 975

Abstract

Photoionization of Cl III ions into Cl IV was studied theoretically using the ab initio relativistic Breit–Pauli R-matrix (BPRM) method and experimentally at the Advanced Light Source (ALS) synchrotron at the Lawrence Berkeley National Laboratory. A relative-ion-yield spectrum of Cl IV was measured [...] Read more.

Photoionization of Cl III ions into Cl IV was studied theoretically using the ab initio relativistic Breit–Pauli R-matrix (BPRM) method and experimentally at the Advanced Light Source (ALS) synchrotron at the Lawrence Berkeley National Laboratory. A relative-ion-yield spectrum of Cl IV was measured with a photon energy resolution of 10 meV. The theoretical study was carried out using a large wave-function expansion of 45 levels of configurations

3 s^{2} 3 p^{2}

,

3 s 3 p^{3}

,

3 s^{2} 3 p 3 d

,

3 s^{2} 3 p 4 s

,

3 s 3 p^{2} 3 d

, and

3 p^{4}

. The resulting spectra are complex. We have compared the observed spectrum with photoionization cross sections (

σ_{P I}

) of the ground state

3 s^{2} 3 p^{3} (^{4} S_{3 / 2}^{o})

and the seven lowest excited levels

3 s^{2} 3 p^{3} (^{2} D_{5 / 2}^{o})

,

3 s^{2} 3 p^{3} (^{2} D_{3 / 2}^{o})

,

3 s^{2} 3 p^{3} (^{2} P_{3 / 2}^{o})

,

3 s^{2} 3 p^{3} (^{2} P_{1 / 2}^{o})

,

3 s 3 p^{4} (^{4} P_{5 / 2})

,

3 s 3 p^{4} (^{4} P_{3 / 2})

and

3 s 3 p^{4} (^{4} P_{1 / 2})

of Cl III, as these can generate resonances within the energy range of the experiment. We were able to identify most of the resonances as belonging to various specific initial levels within the primary Cl III ion beam. Compared to the first five levels, resonant structures in the

σ_{P I}

of excited levels of

3 s 3 p^{4}

appear to have a weaker presence. We have also produced combined theoretical spectra of the levels by convolving the cross sections with a Gaussian profile of experimental width and summing them using statistical weight factors. The theoretical and experimental features show good agreement with the first five levels of Cl III. These features are also expected to elucidate the recent observed spectra of Cl III by Sloan Digital Scan Survey project. Full article

(This article belongs to the Special Issue Photoionization of Atoms)

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21 pages, 1355 KiB

Open AccessArticle

Photoejection from Various Systems and Radiative-Rate Coefficients

by

Anand K. Bhatia

Atoms 2022, 10(1), 9; https://doi.org/10.3390/atoms10010009 - 19 Jan 2022

Cited by 2 | Viewed by 1836

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, [...] Read more.

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 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. Full article

(This article belongs to the Special Issue Photoionization of Atoms)

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19 pages, 557 KiB

Open AccessArticle

Photoionization and Electron-Ion Recombination of n = 1 to Very High n-Values of Hydrogenic Ions

by

Sultana N. Nahar

Atoms 2021, 9(4), 73; https://doi.org/10.3390/atoms9040073 - 03 Oct 2021

Cited by 6 | Viewed by 1388

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 + h

ν \leftrightarrow

H II + e) where H is hydrogen. Studies of these processes have continued [...] Read more.

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 + h

ν \leftrightarrow

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 (

σ_{P I}

), and electron-ion recombination rate coefficients (

α_{R C}

) obtained from recombination cross sections (

σ_{R C}

) for all n values going to a very high value of 800.

σ_{P I}

was obtained using the precise formalism of Burgess and Seaton, and Burgess.

α_{R C}

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

n l

. 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. Full article

(This article belongs to the Special Issue Photoionization of Atoms)

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Review

Jump to: Research

27 pages, 3766 KiB

Open AccessEditor’s ChoiceReview

Photoionization and Electron–Ion Recombination in Astrophysical Plasmas

by

D. John Hillier

Atoms 2023, 11(3), 54; https://doi.org/10.3390/atoms11030054 - 09 Mar 2023

Cited by 3 | Viewed by 1175

Abstract

Photoionization and its inverse, electron–ion recombination, are key processes that influence many astrophysical plasmas (and gasses), and the diagnostics that we use to analyze the plasmas. In this review we provide a brief overview of the importance of photoionization and recombination in astrophysics. [...] Read more.

Photoionization and its inverse, electron–ion recombination, are key processes that influence many astrophysical plasmas (and gasses), and the diagnostics that we use to analyze the plasmas. In this review we provide a brief overview of the importance of photoionization and recombination in astrophysics. We highlight how the data needed for spectral analyses, and the required accuracy, varies considerably in different astrophysical environments. We then discuss photoionization processes, highlighting resonances in their cross-sections. Next we discuss radiative recombination, and low and high temperature dielectronic recombination. The possible suppression of low temperature dielectronic recombination (LTDR) and high temperature dielectronic recombination (HTDR) due to the radiation field and high densities is discussed. Finally we discuss a few astrophysical examples to highlight photoionization and recombination processes. Full article

(This article belongs to the Special Issue Photoionization of Atoms)

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12 pages, 439 KiB

Open AccessReview

Photoionization and Opacity

by

Anil Pradhan

Atoms 2023, 11(3), 52; https://doi.org/10.3390/atoms11030052 - 06 Mar 2023

Cited by 1 | Viewed by 870

Abstract

Opacity determines radiation transport through material media. In a plasma source, the primary contributors to atomic opacity are bound–bound line transitions and bound-free photoionization into the continuum. We review the theoretical methodology for state-of-the-art photoionization calculations based on the R-matrix method as employed [...] Read more.

Opacity determines radiation transport through material media. In a plasma source, the primary contributors to atomic opacity are bound–bound line transitions and bound-free photoionization into the continuum. We review the theoretical methodology for state-of-the-art photoionization calculations based on the R-matrix method as employed in the Opacity Project, the Iron Project, and solution of the heretofore unsolved problem of plasma broadening of autoionizing resonances due to electron impact, Stark (electric microfields), Doppler (thermal), and core-excitations. R-matrix opacity calculations entail huge amount of atomic data and calculations of unprecedented complexity. It is shown that in high-energy-density (HED) plasmas, photoionization cross sections become 3-D energy–temperature–density-dependent owing to considerable attenuation of autoionizing resonance profiles. Hence, differential oscillator strengths and monochromatic opacities are redistributed in energy. Consequently, Rosseland and Planck mean opacities are affected significantly. Full article

(This article belongs to the Special Issue Photoionization of Atoms)

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48 pages, 5260 KiB

Open AccessReview

Measurement of Photoionization Cross-Section for the Excited States of Atoms: A Review

by

Muhammad Aslam Baig

Atoms 2022, 10(2), 39; https://doi.org/10.3390/atoms10020039 - 14 Apr 2022

Cited by 2 | Viewed by 3372

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Photoionization of Atoms)

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19 pages, 2649 KiB

Open AccessReview

Atomic Processes, Including Photoabsorption, Subject to Outside Charge-Neutral Plasma

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Atoms 2022, 10(1), 16; https://doi.org/10.3390/atoms10010016 - 29 Jan 2022

Cited by 5 | Viewed by 2037

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 [...] Read more.

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

V_{D H}

in terms of the Debye length D, which is linked to the ratio between the plasma density N and its temperature

k T

. Our theoretical data generated with

V_{D H}

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. Full article

(This article belongs to the Special Issue Photoionization of Atoms)

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