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A special issue of Atoms (ISSN 2218-2004).

Deadline for manuscript submissions: closed (31 December 2023) | Viewed by 28282

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Prof. Dr. Sultana N. Nahar

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Guest Editor

Astronomy Department, The Ohio State University, Columbus, OH 43210, USA
Interests: photoionization; electron-ion recombination; photo-excitations; electron impact excitation; spectroscopy; X-ray spectroscopy for atomic processes and biomedical applications; database

Prof. Dr. Guillermo Hinojosa

E-Mail Website
Guest Editor

Instituto de Ciencias Físicas, National Autonomous University of Mexico (UNAM), Cuernavaca 62200, Mexico
Interests: atomic, molecular and optical physics; photoionization of ions; negative ions; fundamental processes in low temperature plasma

Special Issue Information

Dear Colleagues,

Photoionization of an atom or ion is one most common processes involving the interaction of a photon with an atom. It is one of the four most dominant atomic processes, along with photo-excitation, electron-ion recombination, and electron impact excitations, in astrophysical plasmas that produce the spectra and hence carries considerable information about the constituent elements and their abundances, plasma opacity, ionization fractions, etc. This special issue will present the precise underlying science of photoionization. Although direct photoionization via absorption of a photon by the atomic system happens, resonances form in the process as the energy of the photon-atom system matches to that of a doubly excited state, known as the autoionizing state, lying above the ionization threshold. It is inherent to study the process with inclusion of resonances. The objective of this issue is to advance the current understanding of atomic photoionization, both theoretically and experimentally, for complex atomic systems with demonstrations of various features in the low and high energy regions, that will impact the accuracy of photoionization environments, modeling of astrophysical and laboratory plasmas and their applications.

Prof. Dr. Sultana N. Nahar
Prof. Dr. Guillermo Hinojosa
Guest Editors

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Keywords

photoionization
experimental features
theoretical features
benchmarking
astrophysical applications

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Published Papers (10 papers)

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Research

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37 pages, 768 KiB

Open AccessArticle

Theoretical Spectra of Lanthanides for Kilonovae Events: Ho I-III, Er I-IV, Tm I-V, Yb I-VI, Lu I-VII

by Sultana N. Nahar

Atoms 2024, 12(4), 24; https://doi.org/10.3390/atoms12040024 - 17 Apr 2024

Cited by 2 | Viewed by 1635

Abstract

The broad emission bump in the electromagnetic spectra observed following the detection of gravitational waves created during the kilonova event of the merging of two neutron stars in August 2017, named GW170817, has been linked to the heavy elements of lanthanides (Z = 57–71) and a new understanding of the creation of heavy elements in the r-process. The initial spectral emission bump has a wavelength range of 3000–7000 Å, thus covering the region of ultraviolet (UV) to optical (O) wavelengths, and is similar to those seen for lanthanides. Most lanthanides have a large number of closely lying energy levels, which introduce extensive sets of radiative transitions that often form broad regions of lines of significant strength. The current study explores these broad features through the photoabsorption spectroscopy of 25 lanthanide ions, Ho I-III, Er I-IV, Tm I-V, Yb I-VI, and Lu I-VII. With excitation only to a few orbitals beyond the ground configurations, we find that most of these ions cover a large number of bound levels with open

4 f

orbitals and produce tens to hundreds of thousands of lines that may form one or multiple broad features in the X-ray to UV, O, and infrared (IR) regions. The spectra of 25 ions are presented, indicating the presence, shapes, and wavelength regions of these features. The accuracy of the atomic data used to interpret the merger spectra is an ongoing problem. The present study aims at providing improved atomic data for the energies and transition parameters obtained using relativistic Breit–Pauli approximation implemented in the atomic structure code SUPERSTRUCTURE and predicting possible features. The present data have been benchmarked with available experimental data for the energies, transition parameters, and Ho II spectrum. The study finds that a number of ions under the present study are possible contributors to the emission bump of GW170817. All atomic data will be made available online in the NORAD-Atomic-Data database. Full article

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

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23 pages, 3642 KiB

Open AccessArticle

Photoionization Study of Neutral Chlorine Atom

by Momar Talla Gning and Ibrahima Sakho

Atoms 2023, 11(12), 152; https://doi.org/10.3390/atoms11120152 - 6 Dec 2023

Cited by 3 | Viewed by 1777

Abstract

Photoionization of neutral chlorine atom is investigated in this paper in the framework of the screening constant per unit nuclear charge (SCUNC) method. Resonance energies, quantum defects and effective charges of the 3s²3p⁴ (³P_2,1,0)ns and 3s²3p⁴ (³P_1,0)nd Rydberg series originating from both the ²P⁰_3/2 ground state and the ²P⁰_1/2 excited state of chlorine atom are reported. The present study believed to be the first theoretical investigation is compared with the recent experimental measurements (Yang et al., Astrophys. J. 810:132, 2015). Good agreements are obtained between theory and experiments. New SCUNC data are tabulated as useful references for interpreting astrophysical spectra from neutral atomic chlorine. Full article

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

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20 pages, 4477 KiB

Open AccessArticle

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

by Jean-Paul Mosnier, Eugene T. Kennedy, Jean-Marc Bizau, Denis Cubaynes, Ségolène Guilbaud, Christophe Blancard, M. Fatih Hasoğlu and Thomas W. Gorczyca

Atoms 2023, 11(4), 66; https://doi.org/10.3390/atoms11040066 - 3 Apr 2023

Cited by 4 | Viewed by 2005

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 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 4 | Viewed by 2224

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 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

by Sultana N. Nahar, Edgar M. Hernández, David Kilcoyne, Armando Antillón, Aaron M. Covington, Olmo González-Magaña, Lorenzo Hernández, Vernon Davis, Dominic Calabrese, Alejandro Morales-Mori, Dag Hanstorp, Antonio M. Juárez and Guillermo Hinojosa

Atoms 2023, 11(2), 28; https://doi.org/10.3390/atoms11020028 - 3 Feb 2023

Cited by 5 | Viewed by 1921

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.

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 2671

Abstract

Photoionization or photodetachment is an important process. It has applications in solar- and astrophysics. In addition to accurate wave function of the target, accurate continuum functions are required. There are various approaches, like exchange approximation, method of polarized orbitals, close-coupling approximation, R-matrix formulation, exterior complex scaling, the recent hybrid theory, etc., to calculate scattering functions. We describe some of them used in calculations of photodetachment or photoabsorption cross sections of ions and atoms. Comparisons of cross sections obtained using different approaches for the ejected electron are given. Furthermore, recombination rate coefficients 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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Review

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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 - 9 Mar 2023

Cited by 6 | Viewed by 2482

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. 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 - 6 Mar 2023

Cited by 5 | Viewed by 1712

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 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 10 | Viewed by 6006

Abstract

A review of experimental studies of the measurement of the photoionization cross-section for the excited states of the alkali atoms, alkaline earth atoms, and rare-gas atoms is presented, with emphasis on using multi-step laser excitation, ionization, and the saturation technique. The dependence of the photoionization cross-section from different intermediate states populated in the first step and ionized in the second step are discussed, including results on the photoionization cross-sections measured above the first ionization threshold. Results based on different polarizations of the exciting and the ionizing dye lasers are also discussed. Examples are provided, illustrating the photoionization cross-sections measured using thermionic diode ion detector, atomic beam apparatus in conjunction with a time-of-flight mass spectrometer and DC/RF glow discharge cell as an optogalvanic detection. 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

by Tu-Nan Chang, Te-Kuei Fang, Chensheng Wu and Xiang Gao

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

Cited by 8 | Viewed by 2866

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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