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Atoms, Volume 12, Issue 11 (November 2024) – 6 articles

Cover Story (view full-size image): The electron transitions in atoms caused by charged particle impact are benchmarks in the study of electron dynamics. In this study, the focus is on the excitation of helium by proton and antiproton impacts. Both ab initio and perturbational calculations are performed, revealing the importance of electron correlations and higher-order effects. The influence of the projectile charge sign on the excitation cross section is also studied. View this paper

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8 pages, 287 KiB

Open AccessArticle

Dataset for Optical Processes in Dense Astrophysical and Laboratory Plasmas

by Nenad M. Sakan, Vladimir A. Srećković, Zoran J. Simić and Momchil Dechev

Atoms 2024, 12(11), 59; https://doi.org/10.3390/atoms12110059 - 14 Nov 2024

Viewed by 846

Abstract

The interest in the modeling of laboratory and astrophysical plasma behavior from mid up to strong non-ideality (NI), e.g., plasma in which a Coulomb interaction becomes dominant, led us to further investigate the optical properties of such systems. An expanded set of results and properties like wave functions, dipole matrix elements, etc., for such systems is presented in this submission. The methodologies of our research, as well as the current and future elements of their applications, are explained. In addition to being helpful to other researchers for achieving a variety of goals, the data from this study could be useful the interdisciplinary fields of machine learning, astrochemistry and fusion physics. The dataset is available online at the repository Figshare. Full article

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9 pages, 430 KiB

Open AccessArticle

On Resonance Enhancement of E1-E2 Nondipole Photoelectron Asymmetries in Low-Energy Ne 2p Photoionization

by Valeriy K. Dolmatov and Steven T. Manson

Atoms 2024, 12(11), 58; https://doi.org/10.3390/atoms12110058 - 7 Nov 2024

Viewed by 815

Abstract

Earlier, a significant enhancement of the nondipole parameters

γ_{2 p}

δ_{2 p}

, and

ζ_{2 p} = γ_{2 p} + 3 δ_{2 p}

in the photoelectron angular distribution for Ne

2 p

photoionization was predicted, owing to [...] Read more.

Earlier, a significant enhancement of the nondipole parameters

γ_{2 p}

δ_{2 p}

, and

ζ_{2 p} = γ_{2 p} + 3 δ_{2 p}

in the photoelectron angular distribution for Ne

2 p

photoionization was predicted, owing to resonance interference between dipole (

E 1

) and quadrupole (

E 2

) transitions. This enhancement manifests as narrow resonance spikes in the parameters due to the low-energy

2 s \to 3 p

and

2 s \to 4 p

dipole, as well as the

2 s \to 3 d

quadrupole autoionizing resonances. Given the unique nature of this predicted enhancement, it requires further validation, specifically regarding whether these narrow spikes in

γ_{2 p}

δ_{2 p}

and

ζ_{2 p}

will or will not retain their values for experimental observation if one accounts for a typical finite frequency spread in the ionizing radiation. To address this, we revisit the previous study, now incorporating the effect of frequency spread in the ionizing radiation, assuming a spread as large as 5 meV at the half-maximum of the radiation’s intensity. In the present paper we demonstrate that while the frequency spread does affect the resonance enhancement of

γ_{2 p}

δ_{2 p}

and

ζ_{2 p}

, these parameters still retain quantitatively significant values to be observed experimentally. The corresponding calculations were performed using the random phase approximation with exchange, which accounts for interchannel coupling in both dipole and quadrupole photoionization amplitudes. Full article

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

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11 pages, 426 KiB

Open AccessArticle

Excitation of Helium by Proton and Antiproton Impact

by Zsuzsánna Bálint, Sándor Borbély and Ladislau Nagy

Atoms 2024, 12(11), 57; https://doi.org/10.3390/atoms12110057 - 3 Nov 2024

Cited by 1 | Viewed by 810

Abstract

The electron transitions in atoms caused by charged particle impact are benchmarks for the study of electron dynamics. In the present paper we focus on the excitation of helium by proton and antiproton impact. We perform both ab initio and perturbational calculations, revealing the importance of electron correlations and higher-order effects. The influence of the projectile charge sign on the excitation cross section is also studied. Full article

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

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14 pages, 361 KiB

Open AccessArticle

On a Study of Photoionization of Atoms and Ions from Endohedral Anions

by Valeriy K. Dolmatov, Larissa V. Chernysheva and Victor G. Yarzhemsky

Atoms 2024, 12(11), 56; https://doi.org/10.3390/atoms12110056 - 30 Oct 2024

Viewed by 895

Abstract

We study the relationship between the results of two qualitatively different semi-empirical models for photoionization cross sections,

σ_{n ℓ}

, of neutral atoms (A) and their cations (

A^{+}

) centrally encapsulated inside a fullerene anion,

C_{N}^{q}

[...] Read more.

We study the relationship between the results of two qualitatively different semi-empirical models for photoionization cross sections,

σ_{n ℓ}

, of neutral atoms (A) and their cations (

A^{+}

) centrally encapsulated inside a fullerene anion,

C_{N}^{q}

, where q represents the negative excess charge on the shell. One of the semi-empirical models, broadly employed in previous studies, assumes a uniform excess negative charge distribution over the entire fullerene cage, by analogy with a charged metallic sphere. The other model, presented here, considers the quantum states of the excess electrons on the shell, determined by specific n and ℓ values of their quantum numbers. Remarkably, both models yield similar photoionization cross sections for the encapsulated species. Consequently, we find that the photoionization of the encapsulated atoms or cations inside the

C_{N}^{q}

anion is influenced only slightly by the quantum states of the excess electrons on the fullerene cage. Furthermore, we demonstrate that the influence decreases even further as the size of the fullerene cage increases. All this holds true at least under the assumption that the encapsulated atom or cation is compact, i.e., its electron density remains primarily within itself rather than being drawn into the fullerene shell. This remarkable finding results from Hartree–Fock calculations combined with a popular modeling of the fullerene shell which is simulated by an attractive spherical annular potential. Full article

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12 pages, 5333 KiB

Open AccessArticle

Impact of Calcium Doping on the Electronic and Optical Characteristics of Strontium Hydride (SrH₂): A DFT Study

by Hamza Errahoui, Mohamed Karouchi, Abdelkebir Ejjabli, Aymane El haji, Abdelmounaim Laassouli, Omar Ait El Alia, Salah Chaji, Youssef Lachtioui and Omar Bajjou

Atoms 2024, 12(11), 55; https://doi.org/10.3390/atoms12110055 - 29 Oct 2024

Cited by 3 | Viewed by 1041

Abstract

This study investigates the electronic and optical properties of calcium-doped strontium hydride (SrH₂) using first-principles density functional theory (DFT) calculations via the CASTEP code with generalized gradient approximation (GGA). We explore the impact of calcium (Ca) doping on the electronic band structure, density of states (DOS), and optical absorption spectra of SrH₂. Our results show that Ca doping significantly alters the electronic properties of SrH₂, notably increasing the indirect bandgap from 1.3 eV to 1.6 eV. The DOS analysis reveals new states near the Fermi level, primarily from Ca 3d orbitals. Moreover, the optical absorption spectra display enhanced absorption in the visible range, suggesting the potential for optoelectronic applications. This research highlights the feasibility of tuning the electronic and optical characteristics of SrH₂ through Ca doping, thus opening the way for the generation of advanced materials with tailored properties. Full article

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

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17 pages, 354 KiB

Open AccessArticle

Gordon Decomposition of the Magnetizability of a Dirac One-Electron Atom in an Arbitrary Discrete Energy State

by Patrycja Stefańska

Atoms 2024, 12(11), 54; https://doi.org/10.3390/atoms12110054 - 25 Oct 2024

Viewed by 4258

Abstract

We present a Gordon decomposition of the magnetizability of a Dirac one-electron atom in an arbitrary discrete energy eigenstate, with a pointlike, spinless, and motionless nucleus of charge

Z e

. The external magnetic field, by which the atomic state is perturbed, is [...] Read more.

We present a Gordon decomposition of the magnetizability of a Dirac one-electron atom in an arbitrary discrete energy eigenstate, with a pointlike, spinless, and motionless nucleus of charge

Z e

. The external magnetic field, by which the atomic state is perturbed, is assumed to be weak, static, and uniform. Using the Sturmian expansion of the generalized Dirac–Coulomb Green function proposed by Szmytkowski in 1997, we derive a closed-form expressions for the diamagnetic (

χ_{d}

) and paramagnetic (

χ_{p}

) contributions to

χ

. Our calculations are purely analytical; the received formula for

χ_{p}

contains the generalized hypergeometric functions ₃F₂ of the unit argument, while

χ_{d}

is of an elementary form. For the atomic ground state, both results reduce to the formulas obtained earlier by other author. This work is a prequel to our recent article, where the numerical values of

χ_{d}

and

χ_{p}

for some excited states of selected hydrogenlike ions with

1 ⩽ Z ⩽ 137

were obtained with the use of the general formulas derived here. Full article

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Atoms, Volume 12, Issue 11 (November 2024) – 6 articles

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