Atoms

12 pages, 819 KB

Open AccessEditor’s ChoiceArticle

Ionization of CF₃CH₂F by Protons and Photons

by Carlos E. Ferreira, Jorge A. de Souza-Corrêa, Alexandre B. Rocha and Antônio C. F. Santos

Atoms 2025, 13(6), 58; https://doi.org/10.3390/atoms13060058 - 18 Jun 2025

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(1) Background: Ionizing radiation in the Earth’s atmosphere drives key chemical transformations affecting atmospheric composition. Despite their environmental relevance, experimental data on proton collisions with hydrofluorocarbons remain limited, and theoretical models for total cross-sections and stopping power are still underdeveloped. (2) Methods: This [...] Read more.

(1) Background: Ionizing radiation in the Earth’s atmosphere drives key chemical transformations affecting atmospheric composition. Despite their environmental relevance, experimental data on proton collisions with hydrofluorocarbons remain limited, and theoretical models for total cross-sections and stopping power are still underdeveloped. (2) Methods: This study applies Rudd’s semiempirical model to calculate proton impact ionization cross-sections for the CF₃CH₂F molecule, considering contributions from both outer and inner electron shells. The model enables the estimation of differential cross-sections and the average energy of secondary electrons. In addition, we calculate the photoionization cross-sections using a discretized representation of the continuum—the so-called pseudo-spectrum—obtained through TDDFT with PBE0 as an exchange–correlation functional and compare it with the cross-section obtained for proton impact in the high-energy limit. (3) Results: The Rudd model proves highly adaptable and suitable for numerical applications. However, its validation is hindered by the scarcity of experimental data. Existing models, such as SRIM and Bethe–Bloch, show significant discrepancies due to their limited applicability at intermediate energies and lack of molecular structure consideration. (4) Conclusions: A comparison between the Rudd and BEB models reveals strong agreement in the analyzed energy range. This consistency stems from both models accounting for the molecular structure of the target, as well as from the fact that protons and electrons possess charges of the same magnitude, supporting a coherent description of ionization processes at these energies. Full article

(This article belongs to the Special Issue Electronic, Photonic and Ionic Interactions with Atoms and Molecules)

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19 pages, 857 KB

Open AccessEditor’s ChoiceArticle

An Explicit Numerical Scheme for Milne’s Phase–Amplitude Equations

by Robin Piron and Mikael Tacu

Atoms 2025, 13(6), 57; https://doi.org/10.3390/atoms13060057 - 18 Jun 2025

Viewed by 392

Abstract

We present an explicit numerical method to solve Milne’s phase–amplitude equations. Existing methods directly solve Milne’s nonlinear equation for amplitude. For that reason, they exhibit high sensitivity to errors and are prone to instability through the growth of a spurious, rapidly varying component [...] Read more.

We present an explicit numerical method to solve Milne’s phase–amplitude equations. Existing methods directly solve Milne’s nonlinear equation for amplitude. For that reason, they exhibit high sensitivity to errors and are prone to instability through the growth of a spurious, rapidly varying component of the amplitude. This makes the systematic use of these methods difficult. On the contrary, the present method is based on solving a linear third-order equation which is equivalent to the nonlinear amplitude equation. This linear equation was derived by Kiyokawa, who used it to obtain analytical results on Coulomb wavefunctions. The present method uses this linear equation for numerical computation, thus resolving the problem of the growth of a rapidly varying component. Full article

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15 pages, 875 KB

Open AccessEditor’s ChoiceArticle

Multi-Configuration Dirac–Hartree–Fock Calculations of Pr⁹⁺ and Nd¹⁰⁺: Configuration Resolution and Probing Fine-Structure Constant Variation

by Songya Zhang, Cunqiang Wu, Chenzhong Dong and Xiaobin Ding

Atoms 2025, 13(6), 54; https://doi.org/10.3390/atoms13060054 - 16 Jun 2025

Viewed by 601

Abstract

We present high-precision multi-configuration Dirac–Hartree–Fock (MCDHF) calculations for the metastable states of

\Pr^{9 +}

and

{Nd}^{10 +}

ions, systematically investigating their energy levels, transition properties, Landé

g_{J}

factors, and hyperfine interaction constants. Our results show excellent agreement with available experimental [...] Read more.

We present high-precision multi-configuration Dirac–Hartree–Fock (MCDHF) calculations for the metastable states of

\Pr^{9 +}

and

{Nd}^{10 +}

ions, systematically investigating their energy levels, transition properties, Landé

g_{J}

factors, and hyperfine interaction constants. Our results show excellent agreement with available experimental data and theoretical benchmarks, while resolving critical configuration assignment discrepancies through detailed angular momentum coupling analysis. The calculations highlight the significant role of Breit interaction and provide the first theoretical predictions of electric quadrupole hyperfine constants (

B_{hfs}

). These findings deliver essential atomic data for the development of next-generation optical clocks and establish lanthanide highly charged ions as exceptional candidates for precision tests of fundamental physics. Full article

(This article belongs to the Special Issue Atomic and Molecular Data and Their Applications: ICAMDATA 2024)

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64 pages, 2080 KB

Open AccessEditor’s ChoiceReview

Triaxial Shapes in Even–Even Nuclei: A Theoretical Overview

by Dennis Bonatsos, Andriana Martinou, Spyridon K. Peroulis, Dimitrios Petrellis, Polytimos Vasileiou, Theodoros J. Mertzimekis and Nikolay Minkov

Atoms 2025, 13(6), 47; https://doi.org/10.3390/atoms13060047 - 31 May 2025

Viewed by 738

Abstract

Triaxial shapes in even–even nuclei have been considered since the early days of the nuclear collective model. Although many theoretical approaches have been used over the years for their description, no effort appears to have been made for grouping them together and identifying [...] Read more.

Triaxial shapes in even–even nuclei have been considered since the early days of the nuclear collective model. Although many theoretical approaches have been used over the years for their description, no effort appears to have been made for grouping them together and identifying regions on the nuclear chart where the appearance of triaxiality might be favored. In addition, over the last few years, discussion has started on the appearance of small triaxiality in nuclei considered so far as purely axial rotors. In the present work, we collect the predictions made by various theoretical approaches and show that pronounced triaxiality appears to be favored within specific stripes on the nuclear chart, with low triaxiality being present in the regions between these stripes, in agreement with parameter-free predictions made by the proxy-SU(3) approximation to the shell model, based on the Pauli principle and the short-range nature of the nucleon–nucleon interaction. The robustness of triaxiality within these stripes is supported by global calculations made in the framework of the Finite-Range Droplet Model (FRDM), which is based on completely different assumptions and possesses parameters fitted in order to reproduce fundamental nuclear properties. Full article

(This article belongs to the Section Nuclear Theory and Experiments)

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12 pages, 9743 KB

Open AccessEditor’s ChoiceArticle

by Peter Van Reeth and John W. Humberston

Atoms 2025, 13(6), 46; https://doi.org/10.3390/atoms13060046 - 28 May 2025

Viewed by 742

Abstract

Scattering differential cross-sections (DCSs) are important tools, both experimentally and theoretically, in the investigation of scattering processes in lepton–atom collisions. In the present work, the elastic scattering differential cross-sections (EDCSs) for e⁺-H and e⁺-He below the first excitation threshold [...] Read more.

Scattering differential cross-sections (DCSs) are important tools, both experimentally and theoretically, in the investigation of scattering processes in lepton–atom collisions. In the present work, the elastic scattering differential cross-sections (EDCSs) for e⁺-H and e⁺-He below the first excitation threshold of the target were evaluated using the Kohn variational method and found to be very similar. In both cases, the EDCS below the positronium formation threshold, i.e., for pure elastic scattering, had minimum valley features in which significant minima close to 90 degrees were found at ≈2.8 eV for H and ≈2 eV for He. These minima were shown to be linked to the zero in the s-wave phase shift, which gives rise to the Ramsauer minimum in the elastic integrated cross-sections. They were not vortices, but the overall EDCS structure was found to be related to the structures and vortices found in the Ps formation differential cross-sections just above the Ps formation threshold. The valley-type structure in the EDCS went smoothly through the Ps formation threshold, where it linked up with a similar valley structure in both the EDCS above the threshold and the Ps formation DCS. A comparison with the EDCS for e⁻-H and e⁻-He scattering over the same energy range revealed similarities with the positron EDCS, however, with less pronounced structures that had different angular and momentum dependences. Full article

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

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14 pages, 1754 KB

Open AccessEditor’s ChoiceArticle

The Single-Active-Electron Approximation with Angular-Momentum-Dependent Potentials: Application to the Helium Atom

by Juan Carlos del Valle and Klaus Bartschat

Atoms 2025, 13(5), 43; https://doi.org/10.3390/atoms13050043 - 14 May 2025

Cited by 1 | Viewed by 1300

Abstract

We discuss an extension of the Single-Active-Electron (SAE) approximation in atoms by allowing the model potential to depend on the angular-momentum quantum number ℓ. We refer to this extension as the ℓ-SAE approximation. The main ideas behind ℓ-SAE are illustrated [...] Read more.

We discuss an extension of the Single-Active-Electron (SAE) approximation in atoms by allowing the model potential to depend on the angular-momentum quantum number ℓ. We refer to this extension as the ℓ-SAE approximation. The main ideas behind ℓ-SAE are illustrated using the helium atom as a benchmark system. We show that introducing ℓ-dependent potentials improves the accuracy of key quantities in atomic structure computed from the Time-Independent Schrödinger Equation (TISE), including energies, oscillator strengths, and static and dynamic polarizabilities, compared to the standard SAE approach. Additionally, we demonstrate that the ℓ-SAE approximation is suitable for quantum simulations of light−atom interactions described by the Time-Dependent Schrödinger Equation (TDSE). As an illustration, we simulate High-order Harmonic Generation (HHG) and the three-sideband (3SB) version of the Reconstruction of Attosecond Beating by Interference of Two-photon Transitions (RABBITT) technique, achieving enhanced accuracy comparable to that obtained in all-electron calculations. One of the main advantages of the ℓ-SAE approach is that existing SAE codes can be easily adapted to handle ℓ-dependent potentials without any additional computational cost. Full article

(This article belongs to the Special Issue Ab Initio Calculations in Atomic, Molecular, and Optical Physics: A Tribute to Barry Irwin Schneider)

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13 pages, 1058 KB

Open AccessEditor’s ChoiceArticle

A Novel Approach to Calculate the Range of High-Energy Charged Particles Within a Medium

by Ioannis Psychogios, Stylianos Vasileios Kontomaris, Anna Malamou and Andreas Stylianou

Atoms 2025, 13(5), 38; https://doi.org/10.3390/atoms13050038 - 27 Apr 2025

Viewed by 417

Abstract

The determination of energy loss of charged particles as they pass through a medium and consequently the calculation of their range within the medium are of tremendous importance in various areas of physics from both theoretical and practical perspectives. Previous works have derived [...] Read more.

The determination of energy loss of charged particles as they pass through a medium and consequently the calculation of their range within the medium are of tremendous importance in various areas of physics from both theoretical and practical perspectives. Previous works have derived approximate equations regarding the range of ions within a medium, focusing on providing simple solutions for practitioners in the radiotherapy field that do not require significant computational cost, unlike traditional Monte Carlo methods. These solutions focus on radiotherapy and are limited to specific ions’ initial speeds, which should be up to 0.65c (where c is the speed of light in vacuum). In this paper, solutions for significantly larger initial velocities are explored. A new analytical equation for determining the range of charged particles within a medium for initial velocities between 0.6c and 0.9c is presented. This equation provides excellent results when compared to the accurate numerical solution. Beyond its theoretical and mathematical interest, this solution is also reliable for radiotherapy applications. It provides excellent results for protons with initial energies between 200 MeV and 350 MeV and has the major advantage of being expressed in terms of elementary functions, making its use more straightforward compared to other approaches. Full article

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10 pages, 4390 KB

Open AccessEditor’s ChoiceArticle

The Laboratory Measurement of the Line Ratios in X-Ray Emission Resulting from the Charge Exchange Between Mg¹¹⁺ and Helium

by Kebao Shu, Caojie Shao, Shuo Zhang, Ruitian Zhang, Cheng Qian, Yingli Xue, Mingwu Zhang, Jinlei Tian, Zhenqiang Wang, Xiaolong Zhu, Liangting Sun, Junxia Ran and Deyang Yu

Atoms 2025, 13(4), 34; https://doi.org/10.3390/atoms13040034 - 14 Apr 2025

Viewed by 609

Abstract

The line ratios in X-ray emission resulting from charge exchange between highly charged ions (HCIs) and neutral atoms are not only crucial for accurately modeling astrophysical X-ray emissions but also offer a unique perspective on the charge exchange processes happening during collisions. The [...] Read more.

The line ratios in X-ray emission resulting from charge exchange between highly charged ions (HCIs) and neutral atoms are not only crucial for accurately modeling astrophysical X-ray emissions but also offer a unique perspective on the charge exchange processes happening during collisions. The K X-ray spectra following charge exchange between Mg¹¹⁺ and He are presented for a collision velocity of 1489 km/s (11.5 keV/amu). The spectra were measured by two Silicon Drift Detectors capable of resolving the Mg¹⁰⁺ Kα, Kβ, Kγ, and Kδ+ lines. The line intensity ratios of Kβ, Kγ, and Kδ+ relative to the Kα line, as well as the hardness ratio, were obtained. The experimental results were compared with the theoretical results from a cascade model that utilizes the state cross-sections produced by multichannel Landau–Zener (MCLZ) calculation. It was discovered that the K X-ray spectrum features can be reproduced well by MCLZ theory when the contributions of both single electron capture (SEC) and autoionizing double capture (ADC) processes are included. This finding implies that the ADC feeding mechanism is significant and should be taken into account for the X-ray emission during charge exchange between highly charged ions and multielectron atoms. Full article

(This article belongs to the Special Issue X-Ray Spectroscopy in Astrophysics)

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26 pages, 4050 KB

Open AccessEditor’s ChoiceArticle

Vibrational Excitation of HDO Molecule by Electron Impact

by Mehdi Adrien Ayouz, Alexandre Faure, Ioan F. Schneider, János Zsolt Mezei and Viatcheslav Kokoouline

Atoms 2025, 13(4), 32; https://doi.org/10.3390/atoms13040032 - 8 Apr 2025

Viewed by 449

Abstract

Cross sections and thermally averaged rate coefficients for the vibrational excitation and de-excitation by electron impact on the HDO molecule are computed using a theoretical approach based entirely on first principles. This approach combines scattering matrices obtained from the UK R-matrix codes for [...] Read more.

Cross sections and thermally averaged rate coefficients for the vibrational excitation and de-excitation by electron impact on the HDO molecule are computed using a theoretical approach based entirely on first principles. This approach combines scattering matrices obtained from the UK R-matrix codes for various geometries of the target molecule, three-dimensional vibrational states of HDO, and the vibrational frame transformation. The vibrational states of the molecule are evaluated by solving the Schrödinger equation numerically, without relying on the normal-mode approximation, which is known to be inaccurate for water molecules. As a result, couplings and transitions between the vibrational states of HDO are accurately accounted for. From the calculated cross sections, thermally averaged rate coefficients and their analytical fits are provided. Significant differences between the results for HDO and H₂O are observed. Additionally, an uncertainty assessment of the obtained data is performed for potential use in modeling non-local thermodynamic equilibrium (non-LTE) spectra of water in various astrophysical environments. Full article

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

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10 pages, 2805 KB

Open AccessEditor’s ChoiceArticle

Photoionization of Trans-Fe Ions: Se IV, Se V, and Se VI

by Brendan M. McLaughlin, Joern Wilms and James F. Babb

Atoms 2025, 13(4), 31; https://doi.org/10.3390/atoms13040031 - 8 Apr 2025

Viewed by 488

Abstract

In the present study, the photoionization cross-sections are calculated for the trans-Fe ions Se IV, Se V, and Se VI over a wide energy region for ground and meta-stable states within the Dirac Atomic R-matrix approach (darc). Our cross-section results, [...] Read more.

In the present study, the photoionization cross-sections are calculated for the trans-Fe ions Se IV, Se V, and Se VI over a wide energy region for ground and meta-stable states within the Dirac Atomic R-matrix approach (darc). Our cross-section results, when benchmarked against the available high-resolution measurements taken at the Advanced Light Source (ALS) for Se IV (Ga-like) and Se VI (Cu-like) selenium ions, show good agreement over the entire photon energy investigated. The present high quality cross-section data are suitable for use in many applications in astrophysics. Full article

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9 pages, 2679 KB

Open AccessEditor’s ChoiceArticle

Forced Atom Interferometers in Optical Harmonic Potentials

by Mingjie Xin, Wui Seng Leong, Zilong Chen and Shau-Yu Lan

Atoms 2025, 13(4), 30; https://doi.org/10.3390/atoms13040030 - 3 Apr 2025

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Abstract

We present a study of Doppler-sensitive light-pulse atom interferometers operating within optical dipole potentials, where atomic trajectories are manipulated using momentum transfer from light pulses and optical forces from the trap. Efficient methods are introduced to minimize the inhomogeneous broadening of oscillation frequencies [...] Read more.

We present a study of Doppler-sensitive light-pulse atom interferometers operating within optical dipole potentials, where atomic trajectories are manipulated using momentum transfer from light pulses and optical forces from the trap. Efficient methods are introduced to minimize the inhomogeneous broadening of oscillation frequencies in atoms confined within a three-dimensional optical lattice trap. These techniques enable the preparation of various quantum states, including vacuum, thermal, and squeezed states, for atom interferometry. Additionally, we demonstrate a two-dimensional atom interferometer using a single optical dipole trap, where transverse motion is activated by offsetting the trap position. Our work provides insights into controlling the mechanical motion of neutral atoms in optical harmonic potentials and contributes to advancing applications in quantum sensing and quantum computing. Full article

(This article belongs to the Special Issue Advances in and Prospects for Matter Wave Interferometry)

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26 pages, 414 KB

Open AccessEditor’s ChoiceArticle

Statistics of Quantum Numbers for Non-Equivalent Fermions in Single-j Shells

by Jean-Christophe Pain

Atoms 2025, 13(4), 25; https://doi.org/10.3390/atoms13040025 - 25 Mar 2025

Viewed by 637

Abstract

This work addresses closed-form expressions for the distributions

P (M)

of the magnetic quantum numbers M and

Q (J)

of total angular momentum J for non-equivalent fermions in single-j orbits. Such quantities play an important role in both [...] Read more.

This work addresses closed-form expressions for the distributions

P (M)

of the magnetic quantum numbers M and

Q (J)

of total angular momentum J for non-equivalent fermions in single-j orbits. Such quantities play an important role in both nuclear and atomic physics, through the shell models. Using irreducible representations of the rotation group, different kinds of formulas are presented, involving multinomial coefficients, generalized Pascal triangle coefficients, or hypergeometric functions. Special cases are discussed, and the connections between

P (M)

(and therefore

Q (J)

) and mathematical functions such as elementary symmetric, cyclotomic, and Jacobi polynomials are outlined. Full article

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

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12 pages, 1538 KB

Open AccessEditor’s ChoiceArticle

Properties of a Static Dipolar Impurity in a 2D Dipolar BEC

by Neelam Shukla and Jeremy R. Armstrong

Atoms 2025, 13(3), 24; https://doi.org/10.3390/atoms13030024 - 10 Mar 2025

Viewed by 1228

Abstract

We study a system of ultra-cold dipolar Bose gas atoms confined in a two-dimensional (2D) harmonic trap with a dipolar impurity implanted at the center of the trap. Due to recent experimental progress in dipolar condensates, we focused on calculating properties of dipolar [...] Read more.

We study a system of ultra-cold dipolar Bose gas atoms confined in a two-dimensional (2D) harmonic trap with a dipolar impurity implanted at the center of the trap. Due to recent experimental progress in dipolar condensates, we focused on calculating properties of dipolar impurity systems that might guide experimentalists if they choose to study impurities in dipolar gases. We used the Gross–Pitaevskii formalism solved numerically via the split-step Crank–Nicolson method. We chose parameters of the background gas to be consistent with dysprosium (Dy), one of the strongest magnetic dipoles and of current experimental interest, and used chromium (Cr), erbium (Er), terbium (Tb), and Dy for the impurity. The dipole moments were aligned by an external field along what was chosen to be the z-axis, and we studied 2D confinements that were perpendicular or parallel to the external field. We show density contour plots for the two confinements, 1D cross-sections of the densities, calculated self-energies of the impurities while varying both number of atoms in the condensate and the symmetry of the trap. We also calculated the time evolution of the density of an initially pure system where an impurity is introduced. Our results show that while the self-energy increases in magnitude with increasing number of particles, it is reduced when the trap anisotropy follows the natural anisotropy of the gas, i.e., elongated along the z-axis in the case of parallel confinement. This work builds upon work conducted in Bose gases with zero-range interactions and demonstrates some of the features that could be found when exploring dipolar impurities in 2D Bose gases. Full article

(This article belongs to the Section Cold Atoms, Quantum Gases and Bose-Einstein Condensation)

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10 pages, 816 KB

Open AccessEditor’s ChoiceArticle

Theoretical Investigation on Vortex Electron Impact Excitation of a Mg Atom Confined in a Solid-State Environment

by Sophia Strnat, Aloka K. Sahoo, Lalita Sharma, Jonas Sommerfeldt, Daesung Park, Christian Bick and Andrey Surzhykov

Atoms 2025, 13(3), 23; https://doi.org/10.3390/atoms13030023 - 24 Feb 2025

Viewed by 937

Abstract

We present a theoretical investigation of the inelastic scattering of vortex electrons by many-electron atoms embedded in a solid-state environment. Special emphasis is placed on the probability of exciting a target atom and on the relative population of its magnetic substates as described [...] Read more.

We present a theoretical investigation of the inelastic scattering of vortex electrons by many-electron atoms embedded in a solid-state environment. Special emphasis is placed on the probability of exciting a target atom and on the relative population of its magnetic substates as described by the set of alignment parameters. These parameters are directly related to the angular distribution of the subsequent radiative decay. To demonstrate the application of the developed theoretical approach, we present calculations for the

3 s^{2} {}^{1}S_{0} \to 3 s 3 p {}^{3}P_{1}

excitation of a Mg atom and its subsequent

3 s 3 p {}^{3}P_{1} \to 3 s^{2} {}^{1}S_{0}

radiative decay. Our results highlight the significance of the orbital angular momentum (OAM) projection as well as the relative position of the vortex electron with respect to the target atom. Full article

(This article belongs to the Special Issue 21st International Conference on the Physics of Highly Charged Ions)

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13 pages, 6452 KB

Open AccessEditor’s ChoiceArticle

Evaluation of Spatial Profile of Local Emissions from W¹⁷⁺–W²³⁺ Unresolved Transition Array Spectra

by Ryota Nishimura, Tetsutarou Oishi, Izumi Murakami, Daiji Kato, Hiroyuki A. Sakaue, Hayato Ohashi, Shivam Gupta, Chihiro Suzuki, Motoshi Goto, Yasuko Kawamoto, Tomoko Kawate, Hiroyuki Takahashi and Kenji Tobita

Atoms 2025, 13(2), 21; https://doi.org/10.3390/atoms13020021 - 18 Feb 2025

Cited by 1 | Viewed by 658

Abstract

Tungsten (W) spectroscopy has attracted significant attention because W is one of the major impurities in ITER and future DEMO reactors. W²²⁺–W³³⁺ spectra at 15–45 Å have been useful for impurity diagnostics. Unresolved Transition Array (UTA) spectra around 200 Å, [...] Read more.

Tungsten (W) spectroscopy has attracted significant attention because W is one of the major impurities in ITER and future DEMO reactors. W²²⁺–W³³⁺ spectra at 15–45 Å have been useful for impurity diagnostics. Unresolved Transition Array (UTA) spectra around 200 Å, which contain W¹⁷⁺–W²³⁺, have potential for diagnostics tungsten ions in even lower charge states. Because multiple charge states overlap with very similar wavelengths, it is challenging to evaluate impurity spatial profiles from UTA spectra around 200 Å. In this study, we conducted tungsten pellet injection experiments in Large Helical Device (LHD) and attempted to evaluate the spatial profiles of UTA spectra around 200 Å, observed at 0.3–0.8 keV of central electron temperature. The results indicated that tungsten ions around W²⁰⁺ were locally profiled in a radial region, r_eff = 0.38 m, where the local electron temperature decreases by 30% to 40% with respect to more central and outer temperatures. These results suggested that the UTA spectrum around 200 Å would be useful for diagnostics of tungsten impurities in lower charge states than the charge states contained in UTA spectra around 15–45 Å. Full article

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

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14 pages, 749 KB

Open AccessEditor’s ChoiceArticle

Modelling of X-Ray Spectra Originating from the He- and Li-like Ni Ions for Plasma Electron Temperature Diagnostics Purposes

by Karol Kozioł, Andrzej Brosławski and Jacek Rzadkiewicz

Atoms 2025, 13(2), 18; https://doi.org/10.3390/atoms13020018 - 9 Feb 2025

Viewed by 752

Abstract

The multi-configurational Dirac–Hartree–Fock method has been used to examine the electron correlation effect on wavelengths and transition rates for

L \to K

transitions occurring in He- and Li-like nickel ions. The collisional-radiative modelling approach has been used to simulate the X-ray spectra, in [...] Read more.

The multi-configurational Dirac–Hartree–Fock method has been used to examine the electron correlation effect on wavelengths and transition rates for

L \to K

transitions occurring in He- and Li-like nickel ions. The collisional-radiative modelling approach has been used to simulate the X-ray spectra, in a 1.585–1.620 Å wavelength range, originating from the He-like nickel ions and their dielectronic Li-, Be-, and B-like satellites for various electron temperature values in the 2 keV to 8 keV range. The presented results may be useful in improving the plasma electron temperature diagnostics based on nickel spectra. Full article

(This article belongs to the Special Issue Atom and Plasma Spectroscopy)

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18 pages, 1928 KB

Open AccessEditor’s ChoiceArticle

Calculated Transition Probabilities for Os VI Spectral Lines of Interest to Nuclear Fusion Research

by Maxime Brasseur, Patrick Palmeri and Pascal Quinet

Atoms 2025, 13(2), 11; https://doi.org/10.3390/atoms13020011 - 21 Jan 2025

Viewed by 963

Abstract

In this work, we present a new set of transition probabilities for experimentally classified spectral lines in the Os VI spectrum. To do this, two independent computational approaches based on the pseudo-relativistic Hartree–Fock, including core polarization effects (HFR+CPOL) and fully relativistic Multiconfiguration Dirac–Hartree–Fock [...] Read more.

In this work, we present a new set of transition probabilities for experimentally classified spectral lines in the Os VI spectrum. To do this, two independent computational approaches based on the pseudo-relativistic Hartree–Fock, including core polarization effects (HFR+CPOL) and fully relativistic Multiconfiguration Dirac–Hartree–Fock (MCDHF) methods, were used, with the detailed comparison of the results obtained with these two approaches allowing us to estimate the quality of the calculated radiative parameters. These atomic data, corresponding to 367 lines of five-times ionized osmium between 438.720 and 1486.275 Å, are expected to be useful for the analysis of the spectra emitted by fusion plasmas in which osmium could appear as a result of transmutation by the neutron bombardment of tungsten used as component of the reactor wall, such as the ITER divertor. Full article

(This article belongs to the Special Issue Atom and Plasma Spectroscopy)

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11 pages, 1889 KB

Open AccessEditor’s ChoiceArticle

Chemical Lasers Based on Polyatomic Reaction Dynamics: Research of Vibrational Excitation in a Reactive

by José Daniel Sierra Murillo

Atoms 2025, 13(1), 5; https://doi.org/10.3390/atoms13010005 - 9 Jan 2025

Cited by 1 | Viewed by 852

Abstract

The research presented by the author investigates a polyatomic reaction occurring in the gas phase. This study employs the Quasi-Classical Trajectory (QCT) approach using the Wu–Schatz–Lendvay–Fang–Harding (WSLFH) potential energy surface (PES), recognized as one of the most reliable PES models for this type [...] Read more.

The research presented by the author investigates a polyatomic reaction occurring in the gas phase. This study employs the Quasi-Classical Trajectory (QCT) approach using the Wu–Schatz–Lendvay–Fang–Harding (WSLFH) potential energy surface (PES), recognized as one of the most reliable PES models for this type of analysis. The substantial sample size enables the derivation of detailed results that corroborate previous findings while also identifying potential objectives for future experimental work. The Gaussian Binning (GB) technique is utilized to more effectively highlight the variation in the total angular momentum (J′) of the excited product molecule, HOD*. A key aim of the study is to explore the reaction dynamics due to their importance in excitation and emission processes, which may contribute to the development of a chemical laser based on this reaction. Increasing the vibrational level, v, of one reactant, D₂, significantly enhances the excitation of HOD* and shifts the P(J′) distributions towards higher J′ values, while also broadening the distribution. Although the current research focuses on a few initial conditions, the author plans to extend the study to encompass a wider range of initial conditions within the reaction chamber of this type of chemical laser. Full article

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12 pages, 617 KB

Open AccessEditor’s ChoiceArticle

Exploring the Nuclear Chart via Precision Mass Spectrometry with the TITAN MR-TOF MS

by Annabelle Czihaly, Soenke Beck, Julian Bergmann, Callum L. Brown, Thomas Brunner, Timo Dickel, Jens Dilling, Eleanor Dunling, Jake Flowerdew, Danny Fusco, Leigh Graham, Zach Hockenbery, Chris Izzo, Andrew Jacobs, Brian Kootte, Yang Lan, Stephan Malbrunot-Ettenauer, Fernando Maldonado Millán, Ali Mollaebrahimi, Erich Leistenschneider, Eleni Marina Lykiardopoulou, Ish Mukul, Stefan F. Paul, Wolfgang R. Plaß, Moritz Pascal Reiter, Christoph Scheidenberger, James L. Tracy, Jr. and A. A. Kwiatkowski Show full author list Hide full author list

Atoms 2025, 13(1), 6; https://doi.org/10.3390/atoms13010006 - 9 Jan 2025

Viewed by 1241

Abstract

Isotopes at the limits of nuclear existence are of great interest for their critical role in nuclear astrophysical reactions and their exotic structure. Experimentally, exotic nuclides are challenging to address due to their low production cross-sections, overwhelming amounts of contamination, and lifetimes of [...] Read more.

Isotopes at the limits of nuclear existence are of great interest for their critical role in nuclear astrophysical reactions and their exotic structure. Experimentally, exotic nuclides are challenging to address due to their low production cross-sections, overwhelming amounts of contamination, and lifetimes of typically less than a second. To this end, a Multiple-Reflection Time-of-Flight mass spectrometer at the TITAN-TRIUMF facility was built to determine atomic masses. This device is the preferred tool to work with exotic nuclides due to its ability to resolve the species of interest from contamination and short measurement cycle times, enabling mass measurements of isotopes with millisecond half-lives. With a relative precision of the order 10⁻⁷, we demonstrate why the TITAN MR-TOF MS is the tool of choice for precision mass surveys for nuclear structure and astrophysics. The capabilities of the device are showcased in this work, including new mass measurements of short-lived tin isotopes (^104–107Sn) approaching the proton dripline as well as ⁸⁹Zr, ⁹⁰Y, and ⁹¹Y. The last three illustrate how the broadband surveys of MR-TOF MS reach beyond the species of immediate interest. Full article

(This article belongs to the Special Issue Advances in Ion Trapping of Radioactive Ions)

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13 pages, 1408 KB

Open AccessEditor’s ChoiceArticle

Cooper Pairs in 2D Trapped Atoms Interacting Through Finite-Range Potentials

by Erick Manuel Pineda-Ríos and Rosario Paredes

Atoms 2025, 13(1), 4; https://doi.org/10.3390/atoms13010004 - 7 Jan 2025

Viewed by 1148

Abstract

This work deals with the key constituent behind the existence of superfluid states in ultracold fermionic gases confined in a harmonic trap in 2D, namely, the formation of Cooper pairs in the presence of a Fermi sea in inhomogeneous confinement. For a set [...] Read more.

This work deals with the key constituent behind the existence of superfluid states in ultracold fermionic gases confined in a harmonic trap in 2D, namely, the formation of Cooper pairs in the presence of a Fermi sea in inhomogeneous confinement. For a set of finite-range models representing particle–particle interaction, we first ascertain the simultaneity of the emergence of bound states and the divergence of the s-wave scattering length in 2D as a function of the interaction potential parameters in free space. Then, through the analysis of two particles interacting in 2D harmonic confinement, we evaluate the energy shift with respect to the discrete harmonic oscillator levels for both repulsive and attractive cases. All of these results are the basis for determining the energy gaps of Cooper pairs arising from two particles interacting in the presence of a Fermi sea consisting of particles immersed in a 2D harmonic trap. Full article

(This article belongs to the Special Issue Quantum Technologies with Cold Atoms)

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11 pages, 1434 KB

Open AccessEditor’s ChoiceArticle

Emergence of Quantum Vortices in the Ionization of Helium by Proton Impact, and How to Measure Them

by Tamara A. Guarda, Francisco Navarrete and Raúl O. Barrachina

Atoms 2025, 13(1), 3; https://doi.org/10.3390/atoms13010003 - 6 Jan 2025

Viewed by 1141

Abstract

This study investigates how the presence of quantum vortices affects the ionization cross-section of helium atoms by 75 keV proton impact, with special attention to the region near the electron capture to the continuum (ECC) cusp. It has been found that these vortices [...] Read more.

This study investigates how the presence of quantum vortices affects the ionization cross-section of helium atoms by 75 keV proton impact, with special attention to the region near the electron capture to the continuum (ECC) cusp. It has been found that these vortices cause a significant reduction in the intensity of the

{| T |}^{2}

distribution in the low-energy region of the ECC cusp, leading to a considerable distortion that facilitates its experimental determination. Furthermore, the analysis shows that one of the vortices coincides with the Thomas angle (a parameter coming from the classical ion-electron Thomas mechanism). Full article

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11 pages, 260 KB

Open AccessEditor’s ChoiceArticle

Nuclear Hyperfine Mixing Effect in Highly Charged ²⁰⁵Pb Ions

by Wu Wang, Yong Li and Xu Wang

Atoms 2025, 13(1), 2; https://doi.org/10.3390/atoms13010002 - 3 Jan 2025

Cited by 1 | Viewed by 853

Abstract

In highly charged ions, significant nuclear hyperfine mixing (NHM) effects can arise when the electromagnetic field generated by the electrons interacts strongly with the nucleus, leading to mixing of nuclear states. While previous studies have primarily attributed the NHM effect to unpaired valence [...] Read more.

In highly charged ions, significant nuclear hyperfine mixing (NHM) effects can arise when the electromagnetic field generated by the electrons interacts strongly with the nucleus, leading to mixing of nuclear states. While previous studies have primarily attributed the NHM effect to unpaired valence electrons, we present a reformulation of the theoretical framework using dressed hyperfine states and investigate the NHM effect in ²⁰⁵Pb⁷⁶⁺, ²⁰⁵Pb⁷⁵⁺, ²⁰⁵Pb⁷⁴⁺, and ²⁰⁵Pb⁷³⁺ ions. Our numerical results show that significant NHM effects occurred in all of the studied ions, even in the absence of unpaired valence electrons in ²⁰⁵Pb⁷⁶⁺ and ²⁰⁵Pb⁷⁴⁺. We found that the lifetime of the isomeric state was reduced by 2–4 orders of magnitude compared with the bare ²⁰⁵Pb nucleus, depending on the charge state of the ion. These results indicate that it is the active valence electrons rather than unpaired electrons which play a key role in the NHM effect, thereby deepening our understanding of this phenomenon. Full article

(This article belongs to the Special Issue 21st International Conference on the Physics of Highly Charged Ions)

9 pages, 1256 KB

Open AccessEditor’s ChoiceArticle

Double and Triple Photoionization of CCl₄

by Antônio Carlos Fontes dos Santos, Joselito Barbosa Maciel, Alexandre Braga Rocha and Gerardo Gerson Bezerra de Souza

Atoms 2024, 12(12), 74; https://doi.org/10.3390/atoms12120074 - 21 Dec 2024

Viewed by 757

Abstract

(1) Background: Fragmentation after double and triple photoionization of the CCl₄ molecule in the valence, Cl 2p, and C 1s regions have been reported; (2) Methods: We have used photoion-photoion (PIPICO) coincidence technique combined with synchrotron radiation. In addition, [...] Read more.

(1) Background: Fragmentation after double and triple photoionization of the CCl₄ molecule in the valence, Cl 2p, and C 1s regions have been reported; (2) Methods: We have used photoion-photoion (PIPICO) coincidence technique combined with synchrotron radiation. In addition, ab initio quantum mechanical calculations were done at multiconfigurational self-consistent and multireference configuration interaction to describe ground and inner-shell states; (3) Results: We have observed coincidences involving singly and doubly charged fragments coming from the doubly and triply ionized molecule. We have also found a well agreement between the quantum mechanical calculations and the total ion yield spectrum. It is shown that the Cl⁺ ion is the predominant product resulting from the fragmentation of the doubly and triply charged CCl₄ molecule. The CCl⁺ + Cl⁺ pair is the dominant coincidence in the spectra from valence up to the C 1s edge; (4) Conclusions: The kinetic energy of the fragments is compatible with the Coulomb explosion model. Full article

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

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23 pages, 9832 KB

Open AccessEditor’s ChoiceArticle

Ion Manipulation from Liquid Xe to Vacuum: Ba-Tagging for a nEXO Upgrade and Future 0νββ Experiments

by Dwaipayan Ray, Robert Collister, Hussain Rasiwala, Lucas Backes, Ali V. Balbuena, Thomas Brunner, Iroise Casandjian, Chris Chambers, Megan Cvitan, Tim Daniels, Jens Dilling, Ryan Elmansali, William Fairbank, Daniel Fudenberg, Razvan Gornea, Giorgio Gratta, Alec Iverson, Anna A. Kwiatkowski, Kyle G. Leach, Annika Lennarz, Zepeng Li, Melissa Medina-Peregrina, Kevin Murray, Kevin O’Sullivan, Regan Ross, Raad Shaikh, Xiao Shang, Joseph Soderstrom, Victor Varentsov and Liang Yang Show full author list Hide full author list

Atoms 2024, 12(12), 71; https://doi.org/10.3390/atoms12120071 - 19 Dec 2024

Cited by 3 | Viewed by 1191

Abstract

Neutrinoless double beta decay (

0 ν β β

) provides a way to probe physics beyond the Standard Model of particle physics. The upcoming nEXO experiment will search for

0 ν β β

decay in ¹³⁶Xe with a projected half-life sensitivity [...] Read more.

Neutrinoless double beta decay (

0 ν β β

) provides a way to probe physics beyond the Standard Model of particle physics. The upcoming nEXO experiment will search for

0 ν β β

decay in ¹³⁶Xe with a projected half-life sensitivity exceeding

10^{28}

years at the 90% confidence level using a liquid xenon (LXe) Time Projection Chamber (TPC) filled with 5 tonnes of Xe enriched to ∼90% in the

β β

-decaying isotope ¹³⁶Xe. In parallel, a potential future upgrade to nEXO is being investigated with the aim to further suppress radioactive backgrounds and to confirm

β β

-decay events. This technique, known as Ba-tagging, comprises extracting and identifying the

β β

-decay daughter ¹³⁶Ba ion. One tagging approach being pursued involves extracting a small volume of LXe in the vicinity of a potential

β β

-decay using a capillary tube and facilitating a liquid-to-gas phase transition by heating the capillary exit. The Ba ion is then separated from the accompanying Xe gas using a radio-frequency (RF) carpet and RF funnel, conclusively identifying the ion as ¹³⁶Ba via laser-fluorescence spectroscopy and mass spectrometry. Simultaneously, an accelerator-driven Ba ion source is being developed to validate and optimize this technique. The motivation for the project, the development of the different aspects, along with the current status and results, are discussed here. Full article

(This article belongs to the Special Issue Advances in Ion Trapping of Radioactive Ions)

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19 pages, 495 KB

Open AccessEditor’s ChoiceArticle

State-Selective Double Photoionization of Atomic Carbon and Neon

by Frank L. Yip

Atoms 2024, 12(12), 70; https://doi.org/10.3390/atoms12120070 - 16 Dec 2024

Viewed by 1126

Abstract

Double photoionization (DPI) allows for a sensitive and direct probe of electron correlation, which governs the structure of all matter. For atoms, much of the work in theory and experiment that informs our fullest understanding of this process has been conducted on helium, [...] Read more.

Double photoionization (DPI) allows for a sensitive and direct probe of electron correlation, which governs the structure of all matter. For atoms, much of the work in theory and experiment that informs our fullest understanding of this process has been conducted on helium, and efforts continue to explore many-electron targets with the same level of detail to understand the angular distributions of the ejected electrons in full dimensionality. Expanding on previous results, we consider here the double photoionization of two

2 p

valence electrons of atomic carbon and neon and explore the possible continuum states that are connected by dipole selection rules to the coupling of the outgoing electrons in ³P, ¹D, and ¹S initial states of the target atoms. Carbon and neon share these possible symmetries for the coupling of their valence electrons. Results are presented for the energy-sharing single differential cross section (SDCS) and triple differential cross section (TDCS), further elucidating the impact of the initial state symmetry in determining the angular distributions that are impacted by the correlation that drives the DPI process. Full article

(This article belongs to the Special Issue Ab Initio Calculations in Atomic, Molecular, and Optical Physics: A Tribute to Barry Irwin Schneider)

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11 pages, 983 KB

Open AccessEditor’s ChoiceReview

A Critical Look at Density Functional Theory in Chemistry: Untangling Its Strengths and Weaknesses

by Konstantinos P. Zois and Demeter Tzeli

Atoms 2024, 12(12), 65; https://doi.org/10.3390/atoms12120065 - 11 Dec 2024

Cited by 3 | Viewed by 2406

Abstract

Density functional theory (DFT) is a commonly used methodology favored by experts and non-experts alike. It is a useful tool for the investigation of atomic, molecular and surface systems, offering an efficient and often reliable approach to calculate ground state properties such as [...] Read more.

Density functional theory (DFT) is a commonly used methodology favored by experts and non-experts alike. It is a useful tool for the investigation of atomic, molecular and surface systems, offering an efficient and often reliable approach to calculate ground state properties such as electron density, total energy and molecular structure. However, fundamental issues are not rare. Of course, no one can really question the bold impact of DFT on modern chemical science. It is not only the way research is conducted that has been influenced by DFT, but also textbooks, datasets and our chemical intuition as well. In this review, issues pertaining to DFT are discussed, and it is pointed out that without a clear understanding of why we use calculations, an effective combination of experiment and theory will never be accomplished. Using low-level theoretical frameworks surely does not shed light on profound problems. To excel in our scientific field and make good use of our tools, we must very carefully decide which methodologies we are to employ. Full article

(This article belongs to the Section Quantum Chemistry, Computational Chemistry and Molecular Physics)

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16 pages, 1489 KB

Open AccessEditor’s ChoiceArticle

Theoretical Study of the Dissociative Recombination and Vibrational (De-)Excitation of HCNH⁺ and Its Isomers by Electron Impact

by Mehdi Adrien Ayouz and Arnaud Buch

Atoms 2024, 12(12), 64; https://doi.org/10.3390/atoms12120064 - 3 Dec 2024

Cited by 1 | Viewed by 1130

Abstract

Protonated hydrogen cyanide, HCNH⁺, is one of the most important molecules of interest in the astrophysical and astrochemical fields. This molecule not only plays the role of a reaction intermediary in various types of interstellar reactions but was also identified in [...] Read more.

Protonated hydrogen cyanide, HCNH⁺, is one of the most important molecules of interest in the astrophysical and astrochemical fields. This molecule not only plays the role of a reaction intermediary in various types of interstellar reactions but was also identified in Titan’s upper atmosphere. The cross sections for the dissociative recombination (DR) and vibrational (de-)excitation (VE and VDE) of HCNH⁺ and its

{CNH}_{2}^{+}

isomer are computed using a theoretical approach based on a combination of the normal mode approximation for the vibrational states of the target ions and the UK R-matrix code to evaluate electron-ion scattering matrices for fixed geometries of ions. The theoretical convoluted DR cross section for HCNH⁺ agrees well with the experimental data and a previous study. It was also found that the DR of the

{CNH}_{2}^{+}

isomer is important, which suggests that this ion might be present in DR experiments of HCNH⁺. Moreover, the ab initio calculations performed on the H₂CN⁺ isomer predict that this ion is a transition state. This result was confirmed by the study of the reaction path of the HCNH⁺ isomerization that was carried out by evaluating the intrinsic reaction coordinate (IRC). Finally, thermally averaged rate coefficients derived from the cross sections are provided for temperatures in the 10–10,000 K range. A comprehensive set of calculations is performed to assess the uncertainty of the obtained data. These results should help in modeling non-LTE spectra of HCNH⁺, taking into account the role of its most stable isomer, in various astrophysical environments. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms and Molecules in Ionized Environments)

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12 pages, 456 KB

Open AccessEditor’s ChoiceArticle

Mutual Neutralization in Collisions of Li⁺ with O⁻

by Åsa Larson and Ann E. Orel

Atoms 2024, 12(12), 61; https://doi.org/10.3390/atoms12120061 - 28 Nov 2024

Viewed by 721

Abstract

The total and differential cross-sections and final state distribution for mutual neutralization in collisions of Li⁺ with O⁻ were calculated using an ab initio quantum mechanical approach based on potential energy curves and non-adiabatic coupling elements computed with the multi-reference configuration [...] Read more.

The total and differential cross-sections and final state distribution for mutual neutralization in collisions of Li⁺ with O⁻ were calculated using an ab initio quantum mechanical approach based on potential energy curves and non-adiabatic coupling elements computed with the multi-reference configuration interaction method. The final state distributions favored channels with excited oxygen states, indicating a strong effect of electron correlation, and the electron transfer could not be described by a simple one-electron exchange process. Full article

(This article belongs to the Special Issue Ab Initio Calculations in Atomic, Molecular, and Optical Physics: A Tribute to Barry Irwin Schneider)

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15 pages, 1189 KB

Open AccessEditor’s ChoiceArticle

Application of Atomic Spectroscopy of Trapped Radioactive Ions in Nuclear Physics

by Ruben P. de Groote

Atoms 2024, 12(12), 60; https://doi.org/10.3390/atoms12120060 - 21 Nov 2024

Cited by 1 | Viewed by 1165

Abstract

A review is given of precision measurements of hyperfine constants and nuclear g-factors measured with ions confined in ion traps. The nuclear physics observables which can be extracted from these types of measurements are discussed. The feasibility of future nuclear structure studies [...] Read more.

A review is given of precision measurements of hyperfine constants and nuclear g-factors measured with ions confined in ion traps. The nuclear physics observables which can be extracted from these types of measurements are discussed. The feasibility of future nuclear structure studies using precision atomic spectroscopy of trapped radioactive atoms, produced with accelerator-driven approaches, is discussed. Full article

(This article belongs to the Special Issue Advances in Ion Trapping of Radioactive Ions)

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12 pages, 5333 KB

Open AccessEditor’s ChoiceArticle

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 6 | Viewed by 1366

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 [...] Read more.

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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14 pages, 7071 KB

Open AccessEditor’s ChoiceArticle

Applicability of Bispectral Analysis to Causality Determination within and between Ensembles of Unstable Plasma Waves

by Renaud Stauber and Mark Koepke

Atoms 2024, 12(9), 44; https://doi.org/10.3390/atoms12090044 - 5 Sep 2024

Viewed by 943

Abstract

Turbulence implies nonlinear wave–wave coupling, and determining cause and effect of either is important to understand mixing responsible for enhanced number, momentum, or energy (NME) transport. To explain the identification of parent and daughter modes via a look-up table, we sketch the framework [...] Read more.

Turbulence implies nonlinear wave–wave coupling, and determining cause and effect of either is important to understand mixing responsible for enhanced number, momentum, or energy (NME) transport. To explain the identification of parent and daughter modes via a look-up table, we sketch the framework of bispectral analysis without repeating the mathematical formalism of earlier bispectrum researchers. We then apply this technique to a test signal and plasma fluctuation data from the WVU-Q machine, where the inhomogeneous energy density-driven spectrum exhibited a degree of coupling to lower frequencies that was absent in the case of the related, single-eigenmode, current-driven spectrum. Full article

(This article belongs to the Special Issue Plasma Physics Highlights: Non-equilibrium Dynamics, Interfaces and Mixing)

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15 pages, 734 KB

Open AccessEditor’s ChoiceReview

Electron and Positron Impact Ionization of Molecules

by Ladislau Nagy, István Tóth and Radu I. Campeanu

Atoms 2024, 12(8), 38; https://doi.org/10.3390/atoms12080038 - 23 Jul 2024

Cited by 2 | Viewed by 1436

Abstract

We review our group’s most significant results concerning the collision of positrons and electrons with small molecules. Total and triple differential cross sections for the ionization of these targets were calculated in the distorted wave Born approximation using Gaussian molecular orbitals. Different models [...] Read more.

We review our group’s most significant results concerning the collision of positrons and electrons with small molecules. Total and triple differential cross sections for the ionization of these targets were calculated in the distorted wave Born approximation using Gaussian molecular orbitals. Different models were tested. The obtained theoretical results reproduced, in most cases, the features observed in the experimental data. Full article

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

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19 pages, 475 KB

Open AccessEditor’s ChoiceArticle

Calculations of Positron Scattering from Boron, BH, BF, BF₂, and BF₃

by Nicolas A. Mori, Haadi Umer, Liam H. Scarlett, Igor Bray and Dmitry V. Fursa

Atoms 2024, 12(7), 36; https://doi.org/10.3390/atoms12070036 - 10 Jul 2024

Cited by 3 | Viewed by 1498

Abstract

The single-center convergent close-coupling (CCC) method is applied to calculate positron scattering from boron. A model potential approach is utilized to extract the positronium formation, direct ionization, and values between the positronium formation and ionization thresholds. We present results for total, electron loss, [...] Read more.

The single-center convergent close-coupling (CCC) method is applied to calculate positron scattering from boron. A model potential approach is utilized to extract the positronium formation, direct ionization, and values between the positronium formation and ionization thresholds. We present results for total, electron loss, elastic, momentum transfer, total bound state excitation, positronium formation, direct ionization, stopping power, and mean excitation energy from

10^{- 5}

eV to 5000 eV. For boron, there is only one other set of theoretical positron calculations for elastic and momentum transfer above 500 eV, which is in excellent agreement with the current CCC results. Using the current results for boron atoms and previous CCC calculations for hydrogen and fluorine atoms, positron scattering from BF,

{BF}_{2}

,

{BF}_{3}

, and BH molecules is calculated for energies between 0.1 eV and 5000 eV with a modified independent atom approach. Full article

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

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16 pages, 459 KB

Open AccessEditor’s ChoiceArticle

Experimental and Theoretical Electron Collision Broadening Parameters for Several Ti II Spectral Lines of Industrial and Astrophysical Interest

by Lucía Isidoro-García, Isabel de Andrés-García, Juan Porro, Francisco Fernández and Cristóbal Colón

Atoms 2024, 12(7), 35; https://doi.org/10.3390/atoms12070035 - 9 Jul 2024

Cited by 1 | Viewed by 1651

Abstract

A Q-switched Nd:YAG laser was focused on the Pb–Ti alloy samples in several laser-induced breakdown experiments in order to measure the Stark parameters of several spectral lines (58) of singly ionized titanium, including the 3504.89 Å and 3510.83 Å lines (where we achieved [...] Read more.

A Q-switched Nd:YAG laser was focused on the Pb–Ti alloy samples in several laser-induced breakdown experiments in order to measure the Stark parameters of several spectral lines (58) of singly ionized titanium, including the 3504.89 Å and 3510.83 Å lines (where we achieved new experimental and theoretical values). The diagnostics of the laser-induced plasmas (electron density and electron temperature) were performed using Balmer’s H alpha line (6562.7 Å). The temperatures were obtained by the Boltzmann plot technique with spectral lines of Pb I (after correction for its evident self-absorption). Subsequently, the calculations by the Griem approach of the Stark broadening parameters for several spectral lines were performed using the Gaunt factors proposed by van Regemorter and those proposed by Douglas H. Sampson. In the latter case, the values obtained were very close to the experimental values. This enables us to assume that the calculations performed for the spectral lines of Ti II, without experimental information, are more accurate using the Gaunt factors proposed by Sampson. Full article

(This article belongs to the Special Issue Interaction of Electrons with Atoms and Molecules in Ionized Environments)

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19 pages, 2622 KB

Open AccessEditor’s ChoiceArticle

Sensitivity of a Point-Source-Interferometry-Based Inertial Measurement Unit Employing Large Momentum Transfer and Launched Atoms

by Jinyang Li, Timothy Kovachy, Jason Bonacum and Selim M. Shahriar

Atoms 2024, 12(6), 32; https://doi.org/10.3390/atoms12060032 - 11 Jun 2024

Cited by 1 | Viewed by 1912

Abstract

We analyze theoretically the sensitivity of accelerometry and rotation sensing with a point source interferometer employing large momentum transfer (LMT) and present a design of an inertial measurement unit (IMU) that can measure rotation around and acceleration along each of the three axes. [...] Read more.

We analyze theoretically the sensitivity of accelerometry and rotation sensing with a point source interferometer employing large momentum transfer (LMT) and present a design of an inertial measurement unit (IMU) that can measure rotation around and acceleration along each of the three axes. In this design, the launching technique is used to realize the LMT process without the need to physically change directions of the Raman pulses, thus significantly simplifying the apparatus. We also describe an explicit scheme for such an IMU. Full article

(This article belongs to the Special Issue Advances in and Prospects for Matter Wave Interferometry)

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25 pages, 723 KB

Open AccessEditor’s ChoiceReview

Time-Dependent Density Functional Theory for Atomic Collisions: A Progress Report

by Tom Kirchner

Atoms 2024, 12(6), 31; https://doi.org/10.3390/atoms12060031 - 1 Jun 2024

Viewed by 1864

Abstract

In this paper, the current status of time-dependent density functional theory (TDDFT)-based calculations for ion–atom collision problems is reviewed. Most if not all reported calculations rely on the semiclassical approximation of heavy particle collision physics and the time-dependent Kohn–Sham (TDKS) scheme for computing [...] Read more.

In this paper, the current status of time-dependent density functional theory (TDDFT)-based calculations for ion–atom collision problems is reviewed. Most if not all reported calculations rely on the semiclassical approximation of heavy particle collision physics and the time-dependent Kohn–Sham (TDKS) scheme for computing the electronic density of the system. According to the foundational Runge–Gross theorem, all information available about the electronic many-body system is encoded in the density; however, in practice it is often not known how to extract it without resorting to modelling and approximations. This is in addition to a necessarily approximate implementation of the TDKS scheme due to the lack of precise knowledge about the potential that drives the equations. Notwithstanding these limitations, an impressive body of work has been accumulated over the past few decades. A sample of the results obtained for various collision systems is discussed here, in addition to the formal underpinnings and theoretical and practical challenges of the application of TDDFT to atomic collision problems, which are expounded in mostly nontechnical terms. Open problems and potential future directions are outlined as well. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Atomic Collision and Atomic Spectroscopy)

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16 pages, 386 KB

Open AccessEditor’s ChoiceArticle

Natural Orbitals and Targeted Non-Orthogonal Orbital Sets for Atomic Hyperfine Structure Multiconfiguration Calculations

by Mingxuan Ma, Yanting Li, Michel Godefroid, Gediminas Gaigalas, Jiguang Li, Jacek Bieroń, Chongyang Chen, Jianguo Wang and Per Jönsson

Atoms 2024, 12(6), 30; https://doi.org/10.3390/atoms12060030 - 29 May 2024

Cited by 2 | Viewed by 2109

Abstract

Hyperfine structure constants have many applications, but are often hard to calculate accurately due to large and canceling contributions from different terms of the hyperfine interaction operator, and also from different closed and spherically symmetric core subshells that break up due to electron [...] Read more.

Hyperfine structure constants have many applications, but are often hard to calculate accurately due to large and canceling contributions from different terms of the hyperfine interaction operator, and also from different closed and spherically symmetric core subshells that break up due to electron correlation effects. In multiconfiguration calculations, the wave functions are expanded in terms of configuration state functions (CSFs) built from sets of one-electron orbitals. The orbital sets are typically enlarged within the layer-by-layer approach. The calculations are energy-driven, and orbitals in each new layer of correlation orbitals are spatially localized in regions where the weighted total energy decreases the most, overlapping and breaking up different closed core subshells in an irregular pattern. As a result, hyperfine structure constants, computed as expectation values of the hyperfine operators, often show irregular or oscillating convergence patterns. Large orbital sets, and associated large CSF expansions, are needed to obtain converged values of the hyperfine structure constants. We analyze the situation for the states of the

{2 s^{2} 2 p^{3}, 2 s^{2} 2 p^{2} 3 p, 2 s^{2} 2 p^{2} 4 p}

odd and

{2 s^{2} 2 p^{2} 3 s, 2 s 2 p^{4}, 2 s^{2} 2 p^{2} 4 s, 2 s^{2} 2 p^{2} 3 d}

even configurations in N I, and show that the convergence with respect to the increasing sets of orbitals is radically improved by introducing separately optimized orbital sets targeted for describing the spin- and orbital-polarization effects of the

1 s

and

2 s

core subshells that are merged with, and orthogonalized against, the ordinary energy-optimized orbitals. In the layer-by-layer approach, the spectroscopic orbitals are kept frozen from the initial calculation and are not allowed to relax in response to the introduced layers of correlation orbitals. To compensate for this lack of variational freedom, the orbitals are transformed to natural orbitals prior to the final calculation based on single and double substitutions from an increased multireference set. The use of natural orbitals has an important impact on the states of the

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

configuration, bringing the corresponding hyperfine interaction constants in closer agreement with experiment. Relying on recent progress in methodology, the multiconfiguration calculations are based on configuration state function generators, cutting down the time for spin-angular integration by factors of up to 50, compared to ordinary calculations. Full article

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37 pages, 768 KB

Open AccessEditor’s ChoiceArticle

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 3 | Viewed by 1816

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 = [...] Read more.

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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55 pages, 2293 KB

Open AccessFeature PaperEditor’s ChoiceReview

Atomic Models of Dense Plasmas, Applications, and Current Challenges

by Robin Piron

Atoms 2024, 12(4), 26; https://doi.org/10.3390/atoms12040026 - 17 Apr 2024

Cited by 3 | Viewed by 2388

Abstract

Modeling plasmas in terms of atoms or ions is theoretically appealing for several reasons. When it is relevant, the notion of atom or ion in a plasma provides us with an interpretation scheme of the plasma’s internal functioning. From the standpoint of quantitative [...] Read more.

Modeling plasmas in terms of atoms or ions is theoretically appealing for several reasons. When it is relevant, the notion of atom or ion in a plasma provides us with an interpretation scheme of the plasma’s internal functioning. From the standpoint of quantitative estimation of plasma properties, atomic models of plasma allow one to extend many theoretical tools of atomic physics to plasmas. This notably includes the statistical approaches to the detailed accounting for excited states, or the collisional-radiative modeling of non-equilibrium plasmas, which is based on the notion of atomic processes. This paper is focused on the theoretical challenges raised by the atomic modeling of dense, non-ideal plasmas. It is intended to give a synthetic and pedagogical view on the evolution of ideas in the field, with an accent on the theoretical consistency issues, rather than an exhaustive review of models and experimental benchmarks. First we make a brief, non-exhaustive review of atomic models of plasmas, from ideal plasmas to strongly-coupled and pressure-ionized plasmas. We discuss the limitations of these models and pinpoint some open problems in the field of atomic modeling of plasmas. We then address the peculiarities of atomic processes in dense plasmas and point out some specific issues relative to the calculation of their cross-sections. In particular, we discuss the modeling of fluctuations, the accounting for channel mixing and collective phenomena in the photoabsorption, or the impact of pressure ionization on collisional processes. Full article

(This article belongs to the Special Issue Atomic Physics in Dense Plasmas)

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17 pages, 746 KB

Open AccessEditor’s ChoiceArticle

Enhancement of the NORAD-Atomic-Data Database in Plasma

by Sultana N. Nahar and Guillermo Hinojosa-Aguirre

Atoms 2024, 12(4), 22; https://doi.org/10.3390/atoms12040022 - 9 Apr 2024

Cited by 2 | Viewed by 1933

Abstract

We report recent enhancements to the online atomic database at the Ohio State University, NORAD-Atomic-Data, that provide various parameters for radiative and collisional atomic processes dominant in astrophysical plasma. NORAD stands for Nahar Osu RADiative. The database belongs to the data sources, especially [...] Read more.

We report recent enhancements to the online atomic database at the Ohio State University, NORAD-Atomic-Data, that provide various parameters for radiative and collisional atomic processes dominant in astrophysical plasma. NORAD stands for Nahar Osu RADiative. The database belongs to the data sources, especially for the latest works, of the international collaborations of the Opacity Project and the Iron Project. The contents of the database are calculated values for energies, oscillator strengths, radiative decay rates, lifetimes, cross-sections for photoionization, electron-ion recombination cross-sections, and recombination rate coefficients. We have recently expanded NORAD-Atomic-Data with several enhancements over those reported earlier. They are as follows: (i) We continue to add energy levels, transition parameters, cross-sections, and recombination rates for atoms and ions with their publications. (ii) Recently added radiative atomic data contain a significant amount of transition data for photo-absorption spectral features corresponding to the X-ray resonance fluorescence effect, showing prominent wavelength regions of bio-signature elements, such as phosphorus ions, and emission bumps of heavy elements, such as of lanthanides, which may be created in a kilonova event. We are including (iii) collisional data for electron-impact-excitation, (iv) experimental data for energies and oscillator strengths for line formation, (v) experimental cross-sections for photoionization that can be applied for benchmarking and other applications, and (vi) the introduction of a web-based interactive feature to calculate spectral line ratios at various plasma temperature and density diagnostics, starting with our recently published data for P II. We presented a summary description of theoretical backgrounds for the computed data in the earlier paper. With the introduction of experimental results in the new version of NORAD, we present a summary description of measurement of high-resolution photoionization cross-sections at an Advanced Light Source of LBNL synchrotron set-up and briefly discuss other set-ups. These additions should make NORAD-Atomic-Data more versatile for various applications. For brevity, we provide information on the extensions and avoid repetition of data description of the original paper. Full article

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

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18 pages, 979 KB

Open AccessEditor’s ChoiceArticle

CollisionDB: A New Database of Atomic and Molecular Collisional Processes with an Interactive API

by Christian Hill, Dipti, Kalle Heinola and Martin Haničinec

Atoms 2024, 12(4), 20; https://doi.org/10.3390/atoms12040020 - 27 Mar 2024

Cited by 4 | Viewed by 2346

Abstract

The Atomic and Molecular Data Unit of the International Atomic Energy Agency has developed a new database, CollisionDB, to provide an open, free, robust and long-term repository of data on plasma collisional processes. The database contains data on cross sections and rate coefficients [...] Read more.

The Atomic and Molecular Data Unit of the International Atomic Energy Agency has developed a new database, CollisionDB, to provide an open, free, robust and long-term repository of data on plasma collisional processes. The database contains data on cross sections and rate coefficients for collisions of electrons, photons and heavy particles with atomic and molecular species. A fundamental requirement for this database is the implementation of standardized metadata, which provide an unambiguous description of the collisional data available in peer-reviewed sources. CollisionDB offers both a browser-based search interface and an application programming interface (API) that allows users to filter, process and compare collisional datasets. For this purpose, a Python package PyCollisionDB has been developed to access the CollisionDB API. Here, we present an overview of the technical developments, including data schemas, standards and user interface underlying the CollisionDB application, with particular emphasis on the API developed to support the integration of data into modeling and other codes. Full article

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

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13 pages, 5921 KB

Open AccessEditor’s ChoiceArticle

Line Shape Code Comparison of the Effect of Periodic Fields on Hydrogen Lines

by Ibtissem Hannachi, Spiros Alexiou and Roland Stamm

Atoms 2024, 12(4), 19; https://doi.org/10.3390/atoms12040019 - 22 Mar 2024

Cited by 2 | Viewed by 1794

Abstract

Spectral line shapes code in plasmas (SLSPs) code comparison workshops have been organized in the last decade with the aim of comparing the spectra obtained with independently developed analytical and numerical models. Here, we consider the simultaneous effect of a plasma microfield and [...] Read more.

Spectral line shapes code in plasmas (SLSPs) code comparison workshops have been organized in the last decade with the aim of comparing the spectra obtained with independently developed analytical and numerical models. Here, we consider the simultaneous effect of a plasma microfield and a periodic electric field on the hydrogen lines Lyman-α, Lyman-β, Balmer-α, and Balmer-β for plasma conditions where the Stark effect usually dominates line broadening. Full article

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11 pages, 2109 KB

Open AccessEditor’s ChoiceArticle

Simulation of Extreme Ultraviolet Radiation and Conversion Efficiency of Lithium Plasma in a Wide Range of Plasma Situations

by Xiangdong Li, Frank B. Rosmej and Zhanbin Chen

Atoms 2024, 12(3), 16; https://doi.org/10.3390/atoms12030016 - 12 Mar 2024

Viewed by 2162

Abstract

Based on the detailed term accounting approach, the relationship between extreme ultraviolet conversion efficiency and plasma conditions, which range from 5 to 200 eV for plasma temperature and from 4.63 × 10¹⁷ to 4.63 × 10²² cm⁻³ for plasma density, [...] Read more.

Based on the detailed term accounting approach, the relationship between extreme ultraviolet conversion efficiency and plasma conditions, which range from 5 to 200 eV for plasma temperature and from 4.63 × 10¹⁷ to 4.63 × 10²² cm⁻³ for plasma density, is studied for lithium plasmas through spectral simulations involving very extended atomic configurations, including a benchmark set of autoionizing states. The theoretical limit of the EUV conversion efficiency and its dependence on sustained plasma time are given for different plasma densities. The present study provides the necessary understanding of EUV formation from the perspective of atomic physics and also provides useful knowledge for improving EUV conversion efficiency with different technologies. Full article

(This article belongs to the Special Issue Atomic Physics in Dense Plasmas)

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19 pages, 551 KB

Open AccessEditor’s ChoiceArticle

Prospective Optical Lattice Clocks in Neutral Atoms with Hyperfine Structure

by Tobias Bothwell

Atoms 2024, 12(3), 14; https://doi.org/10.3390/atoms12030014 - 5 Mar 2024

Viewed by 2619

Abstract

Optical lattice clocks combine the accuracy and stability required for next-generation frequency standards. At the heart of these clocks are carefully engineered optical lattices tuned to a wavelength where the differential AC Stark shift between ground and excited states vanishes—the so called ‘magic’ [...] Read more.

Optical lattice clocks combine the accuracy and stability required for next-generation frequency standards. At the heart of these clocks are carefully engineered optical lattices tuned to a wavelength where the differential AC Stark shift between ground and excited states vanishes—the so called ‘magic’ wavelength. To date, only alkaline-earth-like atoms utilizing clock transitions with total electronic angular momentum

J = 0

have successfully realized these magic wavelength optical lattices at the level necessary for state-of-the-art clock operation. In this article, we discuss two additional types of clock transitions utilizing states with

J \neq 0

, leveraging hyperfine structure to satisfy the necessary requirements for controlling lattice-induced light shifts. We propose realizing (i) clock transitions between same-parity clock states with total angular momentum

F = 0

and (ii) M1/E2 clock transitions between a state with

F = 0

and a second state with

J = 1 / 2

,

m_{F} = 0

. We present atomic species which fulfill these requirements before giving a detailed discussion of both manganese and copper, demonstrating how these transitions provide the necessary suppression of fine structure-induced vector and tensor lattice light shifts for clock operations. Such realization of alternative optical lattice clocks promises to provide a rich variety of new atomic species for neutral atom clock operation, with applications from many-body physics to searches for new physics. Full article

(This article belongs to the Special Issue High-Precision Laser Spectroscopy)

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20 pages, 1564 KB

Open AccessEditor’s ChoiceReview

Progress in High-Precision Mass Measurements of Light Ions

by Edmund G. Myers

Atoms 2024, 12(2), 8; https://doi.org/10.3390/atoms12020008 - 26 Jan 2024

Cited by 1 | Viewed by 2102

Abstract

Significant advances in Penning trap measurements of atomic masses and mass ratios of the proton, deuteron, triton, helion, and alpha-particle have occurred in the last five years. These include a measurement of the mass of the deuteron against ¹²C with 8.5 × [...] Read more.

Significant advances in Penning trap measurements of atomic masses and mass ratios of the proton, deuteron, triton, helion, and alpha-particle have occurred in the last five years. These include a measurement of the mass of the deuteron against ¹²C with 8.5 × 10⁻¹² fractional uncertainty; resolution of vibrational levels of H₂⁺ as mass and the application of a simultaneous measurement technique to the H₂⁺/D⁺ cyclotron frequency ratio, yielding a deuteron/proton mass ratio at 5 × 10⁻¹²; new measurements of HD⁺/³He⁺, HD⁺/T⁺, and T⁺/³He⁺ leading to a tritium beta-decay Q-value with an uncertainty of 22 meV, and atomic masses of the helion and triton at 13 × 10⁻¹²; and a new measurement of the mass of the alpha-particle against ¹²C at 12 × 10⁻¹². Some of these results are in strong disagreement with previous values in the literature. Their impact in determining a precise proton/electron mass ratio and electron atomic mass from spectroscopy of the HD⁺ molecular ion is also discussed. Full article

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10 pages, 3617 KB

Open AccessEditor’s ChoiceArticle

Spectral Shift and Split of Harmonic Lines in Propagation Affected High Harmonic Generation in a Long-Interaction Gas Tube

by Jozsef Seres, Enikoe Seres, Carles Serrat, Thanh-Hung Dinh, Noboru Hasegawa, Masahiko Ishino, Masaharu Nishikino and Shinichi Namba

Atoms 2023, 11(12), 150; https://doi.org/10.3390/atoms11120150 - 1 Dec 2023

Cited by 3 | Viewed by 2235

Abstract

While generating high harmonics in long media of helium gas, at certain laser intensities and chirp, the spectral shift and split of the harmonic lines were experimentally observed, sometimes exceeding one harmonic order. Beyond reporting these results, numerical simulations were performed to understand [...] Read more.

While generating high harmonics in long media of helium gas, at certain laser intensities and chirp, the spectral shift and split of the harmonic lines were experimentally observed, sometimes exceeding one harmonic order. Beyond reporting these results, numerical simulations were performed to understand the phenomenon. A 3D propagation model was solved under the strong field approximation. According to the simulations, the distortion of the laser beam profile during propagation and the consequently accused change in the conditions of phase matching are responsible for the observations. The observed phenomena can be an excellent tool to produce tunable narrow band harmonic sources covering a broad range around 13.5 nm for spectroscopy and for seeding X-ray lasers, and to understand non-desired detuning of the seed wavelength. Full article

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13 pages, 3325 KB

Open AccessEditor’s ChoiceArticle

Pathways to the Local Thermodynamic Equilibrium of Complex Autoionizing States

by Frédérick Petitdemange and Frank B. Rosmej

Atoms 2023, 11(11), 146; https://doi.org/10.3390/atoms11110146 - 15 Nov 2023

Viewed by 1838

Abstract

The generally accepted pathway to Local Thermodynamic Equilibrium (LTE) in atomic physics, where collision rates need to be much larger than radiative decay rates, is extended to complex autoionizing states. It is demonstrated that the inclusion of the non-radiative decay (autoionization rate) on [...] Read more.

The generally accepted pathway to Local Thermodynamic Equilibrium (LTE) in atomic physics, where collision rates need to be much larger than radiative decay rates, is extended to complex autoionizing states. It is demonstrated that the inclusion of the non-radiative decay (autoionization rate) on the same footing, like radiative decay, i.e., the LTE criterion

n_{e, c r i t} \times C ≫ A + Γ

(

n_{e, c r i t}

is the critical electron density above which LTE holds,

C

is the collisional rate coefficient, and

A

is the radiative decay rate) is inappropriate for estimating the related critical density. An analysis invoking simultaneously different atomic ionization stages identifies the LTE criteria as a theoretical limiting case, which provides orders of magnitude too high critical densities for almost all practical applications. We introduced a new criterion, where the critical densities are estimated from the non-autoionizing capture states rather than from the autoionizing states. The new criterion is more appropriate for complex autoionizing manifolds and provides order of magnitude reduced critical densities. Detailed numerical calculations are carried out for Na-like states of aluminum, where autoionization to the Ne-like ground and excited state occurrences are in excellent agreement with the new criterion. In addition, a complex multi-electron atomic-level structure and electron–electron correlation are identified as simplifying features rather than aggravating ones for the concept of thermalization. Full article

(This article belongs to the Special Issue Atomic Physics in Dense Plasmas)

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14 pages, 4850 KB

Open AccessEditor’s ChoiceArticle

The Vortex Surface in a Three-Body Quantum System

by Tamara A. Guarda, Francisco Navarrete and Raúl O. Barrachina

Atoms 2023, 11(11), 147; https://doi.org/10.3390/atoms11110147 - 15 Nov 2023

Cited by 1 | Viewed by 2115

Abstract

Vortices are structures known in our daily lives and observed in a wide variety of systems, from cosmic to microscopic scales. Relatively recent studies showed that vortices could also appear in simple quantum systems. For instance, they were observed experimentally and theoretically as [...] Read more.

Vortices are structures known in our daily lives and observed in a wide variety of systems, from cosmic to microscopic scales. Relatively recent studies showed that vortices could also appear in simple quantum systems. For instance, they were observed experimentally and theoretically as isolated zeros in the differential cross section in atomic ionization processes by the impact of charged particles. In this work, we show that the appearance of these quantum vortices as point structures was not due to any intrinsic property of them, but to the use of restrictive geometries in their visualization. In particular, we show that by studying the fully differential cross section for hydrogen ionization by positron impact, these vortex points are actually a manifestation of a more complex and hitherto unexplored structure, a 3D “vortex surface”. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Atomic Collision and Atomic Spectroscopy)

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27 pages, 5680 KB

Open AccessEditor’s ChoiceReview

Collisional Classical Dynamics at the Quantum Scale

by Sebastian Otranto

Atoms 2023, 11(11), 144; https://doi.org/10.3390/atoms11110144 - 9 Nov 2023

Cited by 3 | Viewed by 1945

Abstract

During the past five decades, classical dynamics have been systematically used to gain insight on collision processes between charged particles and photons with atomic and molecular targets. These methods have proved to be efficient for systems in which numerical intensive quantum mechanical methods [...] Read more.

During the past five decades, classical dynamics have been systematically used to gain insight on collision processes between charged particles and photons with atomic and molecular targets. These methods have proved to be efficient for systems in which numerical intensive quantum mechanical methods are not yet tractable. During the years, reaction cross sections for charge exchange and ionization have been scrutinized at the total and differential levels, leading to a clear understanding of the benefits and limitations inherent in a classical description. In this work, we present a review of the classical trajectory Monte Carlo method, its current status and the perspectives that can be envisaged for the near future. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Atomic Collision and Atomic Spectroscopy)

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25 pages, 8162 KB

Open AccessEditor’s ChoiceArticle

Study of Electron Impact Excitation of Na-like Kr Ion for Impurity Seeding Experiment in Large Helical Device

by Shivam Gupta, Tetsutarou Oishi and Izumi Murakami

Atoms 2023, 11(11), 142; https://doi.org/10.3390/atoms11110142 - 5 Nov 2023

Cited by 4 | Viewed by 2682

Abstract

In this work, a krypton gas impurity seeding experiment was conducted in a Large Helical Device. Emission lines from the Na-like Kr ion in the extreme ultraviolet wavelength region, such as 22.00 nm, 17.89 nm, 16.51 nm, 15.99 nm, and 14.08 nm, respective [...] Read more.

In this work, a krypton gas impurity seeding experiment was conducted in a Large Helical Device. Emission lines from the Na-like Kr ion in the extreme ultraviolet wavelength region, such as 22.00 nm, 17.89 nm, 16.51 nm, 15.99 nm, and 14.08 nm, respective to

2 p^{6} 3 p (^{2} P_{1 / 2}^{o}) - 2 p^{6} 3 s (^{2} S_{1 / 2})

,

2 p^{6} 3 p (^{2} P_{3 / 2}^{o}) - 2 p^{6} 3 s (^{2} S_{1 / 2})

,

2 p^{6} 3 d (^{2} D_{3 / 2}) - 2 p^{6} 3 p (^{2} P_{3 / 2}^{o})

,

2 p^{6} 3 d (^{2} D_{5 / 2}) - 2 p^{6} 3 p (^{2} P_{3 / 2}^{o})

, and

2 p^{6} 3 d (^{2} D_{3 / 2}) - 2 p^{6} 3 p (^{2} P_{1 / 2}^{o})

transitions, are observed. In order to generate a theoretical synthetic spectrum, an extensive calculation concerning the excitation of the

{Kr}^{25 +}

ion through electron impact was performed for the development of a suitable plasma model. For this, the relativistic multiconfiguration Dirac–Hartree–Fock method was employed along with its extension to the relativistic configuration interaction method to compute the relativistic bound-state wave functions and excitation energies of the fine structure levels using the General Relativistic Atomic Structure Package-2018. In addition, another set of calculations was carried out utilizing the relativistic many-body perturbation theory and relativistic configuration interaction methods integrated within the Flexible Atomic Code. To investigate the reliability of our findings, the results of excitation energies, transition probabilities, and weighted oscillator strengths of different dipole-allowed transitions obtained from these different methods are presented and compared with the available data. Further, the detailed electron impact excitation cross-sections and their respective rate coefficients are obtained for various fine structure resolved transitions using the fully relativistic distorted wave method. Rate coefficients, calculated using the Flexible Atomic Code for population and de-population kinetic processes, are integrated into the collisional-radiative plasma model to generate a theoretical spectrum. Further, the emission lines observed from the

{Kr}^{25 +}

ion in the impurity seeding experiment were compared with the present plasma model spectrum, demonstrating a noteworthy overall agreement between the measurement and the theoretical synthetic spectrum. Full article

(This article belongs to the Special Issue Atomic Processes for Plasma Modeling Applications)

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