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Interaction of Ionizing Photons with Atomic and Molecular Ions

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

Deadline for manuscript submissions: closed (16 November 2020) | Viewed by 39773

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Special Issue Editors

Prof. Dr. Eugene T. Kennedy

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Guest Editor

School of Physical Sciences, Dublin City University, D09 V209 Dublin 9, Ireland
Interests: photoionization of atomic and molecular ions; applications of laser-produced plasmas; spectroscopy of ions; LIBS

Prof. Dr. John T Costello

E-Mail Website
Guest Editor

School of Physical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland
Interests: photoionization of atomic and molecular ions; applications of laser-produced plasmas; spectroscopy of ions; LIBS

Dr. Jean-Paul Mosnier

E-Mail Website
Guest Editor

Special Issue Information

Dear Colleagues,

Studies of photoionization provide information on the inverse processes of radiative and dielectronic recombination, important in many laboratory and astrophysical plasmas. Problems in upper atmospheric physics and chemistry and new astrophysical observations extending into the X-ray region require continuing laboratory-based experiments to produce key interpretative data.

Laser plasma, HHG, synchrotron, and FEL sources provide complementary capabilities and new theoretical approaches interpret the wide spectrum of results on atomic ions achievable with these light sources. Studies of the photoionization of molecular ions (and variable size clusters) have been initiated and are expected to become of increasing importance in the future.

This Special Issue will include original and review papers over the broad range of photoionization studies achievable with atomic and molecular ions, including experiments on relative and/or absolute cross-sections, linear, and nonlinear behaviors, new instrumental and facility developments, and current theoretical challenges. Studies directed towards important laboratory and astrophysical plasma requirements are also welcome.

Prof. Emeritus Eugene T Kennedy
Prof. John T Costello
Assoc. Prof. Jean-Paul Mosnier
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Atoms is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Photoionization
Photoabsorption
Atomic ions
Molecular ions
Inner-shell
Cross-sections
Multi-photon
Multi-electron
Ion spectroscopy
Short-wavelength light sources
Electron correlations
Photon-ion interactions
Femtosecond
Attosecond
Strong fields
Ultrafast
Astrophysical spectra
Astrophysical processes

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Published Papers (14 papers)

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Editorial

Jump to: Research, Review, Other

4 pages, 191 KiB

Open AccessEditorial

Special Issue “Interaction of Ionizing Photons with Atomic and Molecular Ions”

by Eugene T. Kennedy, John T. Costello and Jean-Paul Mosnier

Atoms 2021, 9(4), 111; https://doi.org/10.3390/atoms9040111 - 13 Dec 2021

Viewed by 2129

Abstract

The interaction of ionizing photons with atoms or ions is a fundamental process in nature, with laboratory, atmospheric and astrophysical implications [...] Full article

(This article belongs to the Special Issue Interaction of Ionizing Photons with Atomic and Molecular Ions)

Research

Jump to: Editorial, Review, Other

18 pages, 2416 KiB

Open AccessArticle

Photoionization Cross-Sections of Carbon-Like N⁺ Near the K-Edge (390–440 eV)

by Jean-Paul Mosnier, Eugene T. Kennedy, Jean-Marc Bizau, Denis Cubaynes, Ségolène Guilbaud, Christophe Blancard and Brendan M. McLaughlin

Atoms 2021, 9(2), 27; https://doi.org/10.3390/atoms9020027 - 11 May 2021

Cited by 4 | Viewed by 3177

Abstract

High-resolution K-shell photoionization cross-sections for the C-like atomic nitrogen ion (N⁺) are reported in the 398 eV (31.15 Å) to 450 eV (27.55 Å) energy (wavelength) range. The results were obtained from absolute ion-yield measurements using the SOLEIL synchrotron radiation facility [...] Read more.

1 s ⟶ 2 p

autoionizing resonance states dominated the cross section spectrum. Analyses of the experimental profiles yielded resonance strengths and Auger widths. In the 415–440 eV photon region

1 s ⟶ (1 s 2 s^{2} 2 p^{2 4} P) n p

and

1 s ⟶ (1 s 2 s^{2} 2 p^{2 2} P) n p

resonances forming well-developed Rydberg series up

n = 7 and n = 8

, respectively, were identified in both the single and double ionization spectra. Theoretical photoionization cross-section calculations, performed using the R-matrix plus pseudo-states (RMPS) method and the multiconfiguration Dirac-Fock (MCDF) approach were bench marked against these high-resolution experimental results. Comparison of the state-of-the-art theoretical work with the experimental studies allowed the identification of new resonance features. Resonance strengths, energies and Auger widths (where available) are compared quantitatively with the theoretical values. Contributions from excited metastable states of the N⁺ ions were carefully considered throughout. Full article

(This article belongs to the Special Issue Interaction of Ionizing Photons with Atomic and Molecular Ions)

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14 pages, 1109 KiB

Open AccessArticle

Multiple Sequential Ionization of Valence n = 4 Shell of Krypton by Intense Femtosecond XUV Pulses

by Elena V. Gryzlova, Maksim D. Kiselev, Maria M. Popova, Anton A. Zubekhin, Giuseppe Sansone and Alexei N. Grum-Grzhimailo

Atoms 2020, 8(4), 80; https://doi.org/10.3390/atoms8040080 - 12 Nov 2020

Cited by 3 | Viewed by 2406

Abstract

Sequential photoionization of krypton by intense extreme ultraviolet femtosecond pulses is studied theoretically for the photon energies below the

3 d

excitation threshold. This regime with energetically forbidden Auger decay is characterized by special features, such as time scaling of the level population. [...] Read more.

Sequential photoionization of krypton by intense extreme ultraviolet femtosecond pulses is studied theoretically for the photon energies below the

3 d

excitation threshold. This regime with energetically forbidden Auger decay is characterized by special features, such as time scaling of the level population. The model is based on the solution of rate equations with photoionization cross sections of krypton in different charge and multiplet states determined using R-matrix calculations. Predictions of the ion yields and photoelectron spectra for various photon fluence are presented and discussed. Full article

(This article belongs to the Special Issue Interaction of Ionizing Photons with Atomic and Molecular Ions)

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21 pages, 3600 KiB

Open AccessArticle

An Investigation of Laser Produced Lead-Tin Alloy Plasmas between 10 and 18 nm

by Enda Scally, Fergal O’Reilly, Patrick Hayden, Isaac Tobin and Gerry O’Sullivan

Atoms 2020, 8(4), 75; https://doi.org/10.3390/atoms8040075 - 20 Oct 2020

Cited by 2 | Viewed by 3074

Abstract

The results of a systematic study performed on Pb-Sn alloys of concentration 65–35% and 94–6% by weight along with spectra from pure Pb and Sn in the wavelength range of 9.8–18 nm are presented. The dynamics of the Nd:YAG laser produced plasma were changed by varying the focused spot size and input energy of the laser pulse; the laser irradiance at the target varied from 7.3 × 10⁹ W cm⁻² to 1.2 × 10¹² W cm⁻². The contributing ion stages and line emission are identified using the steady state collisional radiative model of Colombant and Tonon, and the Cowan suite of atomic structure codes. The Sn spectrum was dominated in each case by the well-known unresolved transition array (UTA) near 13.5 nm. However, a surprising result was the lack of any enhancement or narrowing of this feature at low concentrations of Sn in the alloy spectra whose emission was essentially dominated by Pb ions. Full article

(This article belongs to the Special Issue Interaction of Ionizing Photons with Atomic and Molecular Ions)

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17 pages, 1544 KiB

Open AccessEditor’s ChoiceArticle

Vibrationally and Spin-Orbit-Resolved Inner-Shell X-ray Absorption Spectroscopy of the NH⁺ Molecular Ion: Measurements and ab Initio Calculations

by Stéphane Carniato, Jean-Marc Bizau, Denis Cubaynes, Eugene T. Kennedy, Ségolène Guilbaud, Emma Sokell, Brendan McLaughlin and Jean-Paul Mosnier

Atoms 2020, 8(4), 67; https://doi.org/10.3390/atoms8040067 - 4 Oct 2020

Cited by 12 | Viewed by 3720

Abstract

This article presents N²⁺ fragment yields following nitrogen K-shell photo-absorption in the NH⁺ molecular ion measured at the SOLEIL synchrotron radiation facility in the photon energy region 390–450 eV. The combination of the high sensitivity of the merged-beam, multi-analysis ion apparatus (MAIA) with the high spectral resolution of the PLEIADES beamline helped to resolve experimentally vibrational structures of highly excited [N1s⁻¹H]*⁺ electronic states with closed or open-shell configurations. The assignment of the observed spectral features was achieved with the help of density functional theory (DFT) and post-Hartree Fock Multiconfiguration Self-Consistent-Field/Configuration Interaction (MCSCF/CI) ab-initio theoretical calculations of the N1s core-to-valence and core-to-Rydberg excitations, including vibrational dynamics. New resonances were identified compared to previous work, owing to detailed molecular modeling of the vibrational, spin-orbit coupling and metastable state effects on the spectra. The latter are evidenced by spectral contributions from the ⁴Σ⁻ electronic state which lies 0.07 eV above the NH⁺²Π ground state. Full article

(This article belongs to the Special Issue Interaction of Ionizing Photons with Atomic and Molecular Ions)

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14 pages, 960 KiB

Open AccessEditor’s ChoiceArticle

Spin-Polarized Photoelectron Fluxes from Fullerene Anions

by Valeriy K. Dolmatov

Atoms 2020, 8(4), 65; https://doi.org/10.3390/atoms8040065 - 29 Sep 2020

Cited by 7 | Viewed by 2418

Abstract

Initial insights into spin-polarized photoelectron fluxes from fullerene anions are presented here. Both the angle-dependent and angle-integrated degrees of spin polarization of said photoelectron fluxes are discussed. Empty C

_{60}^{-} (2 p)

and endohedral H@C [...] Read more.

_{60}^{-} (2 p)

and endohedral H@C

_{60}^{-} (2 p)

and He@C

_{60}^{-} (2 p)

anions, where the attached electron resides in a

2 p

state, are chosen as case studies. We uncover the characteristics of the phenomenon in the framework of a semi-empirical methodology where the C

_{60}

cage is modeled by a spherical annular potential, rather than aiming at a rigorous study. It is found that the spin-polarization degree of photoelectron fluxes from fullerene anions can reach large values, including a nearly complete polarization, at/in specific values/domains of the photoelectron momentum. This is shown to correlate with an inherent feature of photoionization of fullerenes, the abundance of resonances, known as confinement resonances, in their photodetachment spectra owing to a large empty space inside fullerenes. Moreover, the results obtained can serve as a touchstone for future studies of the phenomenon by more rigorous theories and/or experiments to reveal the significance of interactions omitted in the present study. Full article

(This article belongs to the Special Issue Interaction of Ionizing Photons with Atomic and Molecular Ions)

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11 pages, 2377 KiB

Open AccessArticle

Modification of a Cylindrical Mirror Analyzer for High Efficiency Photoelectron Spectroscopy on Ion Beams

by Francis Penent, Denis Cubaynes, Pascal Lablanquie, Jérôme Palaudoux, Ségolène Guilbaud, Olivier Moustier, Jérôme Guigand and Jean-Marc Bizau

Atoms 2020, 8(4), 63; https://doi.org/10.3390/atoms8040063 - 25 Sep 2020

Cited by 2 | Viewed by 2819

Abstract

An existing cylindrical mirror analyzer (CMA) that was initially equipped with eight channeltrons detectors has been modified to install large micro-channel plate detectors to perform parallel detection of electrons on an energy range corresponding to ~12% of the mean pass energy. This analyzer is dedicated to photoelectron spectroscopy of ions ionized by synchrotron radiation. The overall detection efficiency is increased by a factor of ~20 compared to the original analyzer. A proof of principle of the efficiency of the analyzer has been done for Xe⁵⁺ and Si⁺ ions and will allow photoelectron spectroscopy on many other ionic species. Full article

(This article belongs to the Special Issue Interaction of Ionizing Photons with Atomic and Molecular Ions)

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9 pages, 388 KiB

Open AccessArticle

Inner-Shell Photodetachment of Na⁻ Using R-Matrix Methods

by T. W. Gorczyca, H.-L. Zhou, A. Hibbert, M. F. Hasoglu and S. T. Manson

Atoms 2020, 8(3), 60; https://doi.org/10.3390/atoms8030060 - 21 Sep 2020

Cited by 1 | Viewed by 2506

Abstract

Inner-shell photodetachment of Na

^{-}

near the L-edge threshold was investigated using the R-matrix method. Significant structure was found in the cross section, and this structure is shown to be related to the complicated correlated electron dynamics endemic in negative ions. Comparison with [...] Read more.

Inner-shell photodetachment of Na

^{-}

(This article belongs to the Special Issue Interaction of Ionizing Photons with Atomic and Molecular Ions)

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8 pages, 1063 KiB

Open AccessArticle

The 5d-6p VUV Photoabsorption Spectrum of Bi⁺

by Hu Lu, Lazaros Varvarezos, Patrick Hayden, Eugene T Kennedy, Jean-Paul Mosnier and John T Costello

Atoms 2020, 8(3), 55; https://doi.org/10.3390/atoms8030055 - 4 Sep 2020

Cited by 2 | Viewed by 2825

Abstract

The photoabsorption spectrum of Bi⁺ was measured in the wavelength range between 37 and 60 nm, using the dual laser plasma technique in which one plasma is used as the source of vacuum ultraviolet continuum radiation and the other plasma is used as the sample of atoms and/or ions to be probed. A number of features in the Bi⁺ spectrum was identified with the aid of the Cowan suite of atomic codes. The 5d → 6p transitions from the ground configuration (5d¹⁰6s²6p²) gave rise to the most prominent features in the measured spectrum. Transitions from low-lying excited states associated with the four excited configurations, 5d¹⁰6s²6p6d, 5d¹⁰6s²6p7s, 5d¹⁰6s²6p7p and 5d¹⁰6s6p³, were found to make small contributions to the observed spectrum in the 47–50 nm spectral region. To the best of our knowledge, for Bi⁺, this spectral region is rather unexplored and spectroscopic data are absent from the literature. Full article

(This article belongs to the Special Issue Interaction of Ionizing Photons with Atomic and Molecular Ions)

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10 pages, 568 KiB

Open AccessArticle

Photoelectron Angular Distributions of Nonresonant Two-Photon Atomic Ionization Near Nonlinear Cooper Minima

by Jiri Hofbrucker, Latifeh Eiri, Andrey V. Volotka and Stephan Fritzsche

Atoms 2020, 8(3), 54; https://doi.org/10.3390/atoms8030054 - 3 Sep 2020

Cited by 4 | Viewed by 2685

Abstract

Photoelectron angular distributions of the two-photon ionization of neutral atoms are theoretically investigated. Numerical calculations of two-photon ionization cross sections and asymmetry parameters are carried out within the independent-particle approximation and relativistic second-order perturbation theory. The dependence of the asymmetry parameters on the polarization and energy of the incident light as well as on the angular momentum properties of the ionized electron are investigated. While dynamic variations of the angular distributions at photon energies near intermediate level resonances are expected, we demonstrate that equally strong variations occur near the nonlinear Cooper minimum. The described phenomena is demonstrated on the example of two-photon ionization of magnesium atom. Full article

(This article belongs to the Special Issue Interaction of Ionizing Photons with Atomic and Molecular Ions)

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14 pages, 434 KiB

Open AccessArticle

Investigation of a Collisional Radiative Model for Laser-Produced Plasmas

by Nicholas L. Wong, Fergal O’Reilly and Emma Sokell

Atoms 2020, 8(3), 52; https://doi.org/10.3390/atoms8030052 - 1 Sep 2020

Cited by 5 | Viewed by 3346 | Correction

Abstract

Plasmas of a variety of types can be described by the collisional radiative (CR) model developed by Colombant and Tonan. From the CR model, the ion distribution of a plasma at a given electron temperature and density can be found. This information is useful for further simulations, and due to this, the employment of a suitable CR model is important. Specifically, ionization bottlenecks, where there are enhanced populations of certain charge states, can be seen in these ion distributions, which in some applications are important in maintaining large amounts of a specific ion. The present work was done by implementing an accepted CR model, proposed by Colombant and Tonon, in Python and investigating the effects of variations in the ionization energy and outermost electron subshell occupancy term on the positions of ionization bottlenecks. Laser Produced Plasmas created using a Nd:YAG laser with an electron density of ∼n_e = 10²¹ cm⁻³ were the focus of this work. Plots of the collisional ionization, radiative recombination, and three-body recombination rate coefficients as well as the ion distribution and peak fractional ion population for various elements were examined. From these results, it is evident that using ionization energies from the NIST database and removing the orbital occupancy term in the CR model produced results with ionization bottlenecks in expected locations. Full article

(This article belongs to the Special Issue Interaction of Ionizing Photons with Atomic and Molecular Ions)

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14 pages, 479 KiB

Open AccessArticle

Effects of the FEL Fluctuations on the 2s2p Li⁺ Auto-Ionization Lineshape

by Tejaswi Katravulapally and Lampros A. A. Nikolopoulos

Atoms 2020, 8(3), 35; https://doi.org/10.3390/atoms8030035 - 14 Jul 2020

Cited by 4 | Viewed by 2829

Abstract

The photoionization of Lithium (Li

^{+}

) via its doubly-excited state 2s2p

^{1} P

The photoionization of Lithium (Li

^{+}

) via its doubly-excited state 2s2p

^{1} P

in intense free electron laser (FEL) radiation is studied. A recently developed perturbative statistical description of the atomic dynamics is used to calculate the ionization yield. It is observed that the FEL temporal fluctuations affect the lineshape significantly, strongly dependent on the product of the pulse’s coherence time with its intensity,

\sim τ_{c} I_{0}

, which is a measure of the effect of the field in one correlation time. The weak-field long-pulse asymmetric resonant Fano-profile is broadened to resemble a Voight profile. As the intensity increases, the subsequent ionization of Li

^{2 +}

takes over and causes further distortion of the lineshape for Li

^{+}

. Full article

(This article belongs to the Special Issue Interaction of Ionizing Photons with Atomic and Molecular Ions)

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Review

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17 pages, 2879 KiB

Open AccessEditor’s ChoiceReview

Photoionization of Astrophysically Relevant Atomic Ions at PIPE

by Stefan Schippers and Alfred Müller

Atoms 2020, 8(3), 45; https://doi.org/10.3390/atoms8030045 - 18 Aug 2020

Cited by 11 | Viewed by 3191

Abstract

We review recent work on the photoionization of atomic ions of astrophysical interest that has been carried out at the photon-ion merged-beams setup PIPE, a permanently installed end station at the XUV beamline P04 of the PETRA III synchrotron radiation source operated by [...] Read more.

^{+}

, Fe

^{2 +}

, and Fe

^{3 +}

ions, and on single and multiple K-shell photoionization of C

^{-}

, C

^{+}

, C

^{4 +}

, Ne

^{+}

, and Si

^{2 +}

ions are discussed in astrophysical contexts. Moreover, these experimental results bear witness of the fact that the implementation of the photon-ion merged-beams method at one of the world’s brightest synchrotron light sources has led to a breakthrough for the experimental study of atomic inner-shell photoionization processes with ions. Full article

(This article belongs to the Special Issue Interaction of Ionizing Photons with Atomic and Molecular Ions)

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