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Atoms, Volume 12, Issue 2 (February 2024) – 6 articles

Cover Story (view full-size image): This comprehensive study, marrying theory and experiment, focuses on single-electron capture via metastable Sn^2+∗ ions from molecular hydrogen, a process of significant relevance for ion mitigation in extreme ultraviolet (EUV) photolithography machines. The semi-classical calculations reveal that at collisional energies pertinent to EUV applications, the cross-section for metastable Sn^2+∗ ions dominates over the one for ground-state Sn²⁺ ions. Experimental validation for Sn^2+∗, extracted from a crossed-beam experiment of Sn³⁺ with hydrogen, demonstrates good agreement with calculations in the 2 to 10 keV range. The investigation discards a significant spin–orbit interaction role and suggests that molecular hydrogen vibrations become pivotal at energies below a few keV. View this paper

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13 pages, 4935 KiB

Open AccessArticle

C_{4} H_{2}^{2 +}

Encompassing Planar Tetracoordinate Iron: Structure and Bonding Patterns

by Shilpa Shajan, Kandasamy Thirunavukkarsu, Vijayanand Chandrasekaran, Venkatesan S. Thimmakondu and Krishnan Thirumoorthy

Atoms 2024, 12(2), 11; https://doi.org/10.3390/atoms12020011 - 18 Feb 2024

Viewed by 1123

Abstract

The singlet, triplet, and quintet electronic states of the Fe

C_{4} H_{2}^{2 +}

system are theoretically explored using quantum chemical methods, and 39 isomers are identified in the singlet electronic state and 4 isomers in both triplet and quintet electronic [...] Read more.

The singlet, triplet, and quintet electronic states of the Fe

C_{4} H_{2}^{2 +}

system are theoretically explored using quantum chemical methods, and 39 isomers are identified in the singlet electronic state and 4 isomers in both triplet and quintet electronic states. A molecule with a planar tetracoordinate iron (ptFe) is found on the potential energy surface of singlet and triplet electronic states. The bonding features of ptFe in the singlet electronic state are analyzed with natural bond orbital (NBO) analysis, adaptive natural density partitioning (AdNDP), and molecular orbital analysis. The resultant data delineate that the ptFe is stabilized through electron delocalization in the ptFe system. Full article

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

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11 pages, 3088 KiB

Open AccessArticle

Optical Extreme Learning Machines with Atomic Vapors

by Nuno A. Silva, Vicente Rocha and Tiago D. Ferreira

Atoms 2024, 12(2), 10; https://doi.org/10.3390/atoms12020010 - 06 Feb 2024

Viewed by 1204

Abstract

Extreme learning machines explore nonlinear random projections to perform computing tasks on high-dimensional output spaces. Since training only occurs at the output layer, the approach has the potential to speed up the training process and the capacity to turn any physical system into a computing platform. Yet, requiring strong nonlinear dynamics, optical solutions operating at fast processing rates and low power can be hard to achieve with conventional nonlinear optical materials. In this context, this manuscript explores the possibility of using atomic gases in near-resonant conditions to implement an optical extreme learning machine leveraging their enhanced nonlinear optical properties. Our results suggest that these systems have the potential not only to work as an optical extreme learning machine but also to perform these computations at the few-photon level, paving opportunities for energy-efficient computing solutions. Full article

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

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11 pages, 351 KiB

Open AccessFeature PaperArticle

Electron Capture from Molecular Hydrogen by Metastable Sn²⁺* Ions

by Klaas Bijlsma, Lamberto Oltra, Emiel de Wit, Luc Assink, Ismanuel Rabadán, Luis Méndez and Ronnie Hoekstra

Atoms 2024, 12(2), 9; https://doi.org/10.3390/atoms12020009 - 01 Feb 2024

Viewed by 1449

Abstract

Over a wide and partly overlapping energy range, the single-electron capture cross-sections for collisions of metastable

{Sn}^{2 +} (5 s 5 p P_{o}^{3})

(

{Sn}^{2 + *}

) ions with

H_{2}

molecules were measured (0.1–10 [...] Read more.

Over a wide and partly overlapping energy range, the single-electron capture cross-sections for collisions of metastable

{Sn}^{2 +} (5 s 5 p P_{o}^{3})

(

{Sn}^{2 + *}

) ions with

H_{2}

molecules were measured (0.1–10 keV) and calculated (0.3–1000 keV). The semi-classical calculations use a close-coupling method on a basis of electronic wavefunctions of the (SnH₂)²⁺ system. The experimental cross-sections were extracted from double collisions in a crossed-beam experiment of

{Sn}^{3 +}

with

H_{2}

. The measured capture cross-sections for

{Sn}^{2 + *}

show good agreement with the calculations between 2 and 10 keV, but increase toward lower energies, whereas the calculations decrease. Additional Landau–Zener calculations were performed and show that the inclusion of spin-orbit splitting cannot explain the large cross-sections at the lowest energies which we now assume to be likely due to vibrational effects in the molecular hydrogen target. Full article

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

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20 pages, 1564 KiB

Open AccessReview

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

Viewed by 1219

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 × 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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18 pages, 1849 KiB

Open AccessArticle

Nanoparticle Interferometer by Throw and Catch

by Jakub Wardak, Tiberius Georgescu, Giulio Gasbarri, Alessio Belenchia and Hendrik Ulbricht

Atoms 2024, 12(2), 7; https://doi.org/10.3390/atoms12020007 - 25 Jan 2024

Viewed by 1372

Abstract

Matter wave interferometry with increasingly larger masses could pave the way to understanding the nature of wavefunction collapse, the quantum to classical transition, or even how an object in a spatial superposition interacts with its gravitational field. In order to improve upon the current mass record, it is necessary to move into the nanoparticle regime. In this paper, we provide a design for a nanoparticle Talbot–Lau matter wave interferometer that circumvents the practical challenges of previously proposed designs. We present numerical estimates of the expected fringe patterns that such an interferometer would produce, considering all major sources of decoherence. We discuss the practical challenges involved in building such an experiment, as well as some preliminary experimental results to illustrate the proposed measurement scheme. We show that such a design is suitable for seeing interference fringes with

10^{6}

amu SiO₂ particles and that this design can be extended to even

10^{8}

amu particles by using flight times below the typical Talbot time of the system. Full article

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

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15 pages, 2708 KiB

Open AccessArticle

New Data on Autoionizing States of Ne Induced by Low-Energy Electrons from 45 to 64 eV

by Jozo J. Jureta, Bratislav P. Marinković and Lorenzo Avaldi

Atoms 2024, 12(2), 6; https://doi.org/10.3390/atoms12020006 - 23 Jan 2024

Viewed by 1296

Abstract

The lowest single and doubly excited autoionizing states of neon have been studied using a non-monochromatic electron beam and a high-resolution electrostatic analyzer at incident electron energies from 43.37 to 202 (±0.4) eV at three ejection angles, 40°, 90° and 130°. The 2s2p⁶3s(^3,1S) and 2s2p⁶3p(^3,1P) as well as the 2p⁴3s3p doubly excited states have been observed and their energy determined. The influence of the PCI effect in the energy region of the 2s2p⁶3s(^3,1S) states has been investigated. New features in the ejected electron spectra in the low kinetic energy region 3–20 eV at 202 eV incident energy have been observed and assigned. Full article

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Atoms, Volume 12, Issue 2 (February 2024) – 6 articles

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