Atoms

15 pages, 2130 KiB

Open AccessEditor’s ChoiceArticle

Long-Range Atom–Ion Rydberg Molecule: A Novel Molecular Binding Mechanism

by Markus Deiß, Shinsuke Haze and Johannes Hecker Denschlag

Atoms 2021, 9(2), 34; https://doi.org/10.3390/atoms9020034 - 21 Jun 2021

Cited by 26 | Viewed by 3836

We present a novel binding mechanism where a neutral Rydberg atom and an atomic ion form a molecular bound state at a large internuclear distance. The binding mechanism is based on Stark shifts and level crossings that are induced in the Rydberg atom [...] Read more.

We present a novel binding mechanism where a neutral Rydberg atom and an atomic ion form a molecular bound state at a large internuclear distance. The binding mechanism is based on Stark shifts and level crossings that are induced in the Rydberg atom due to the electric field of the ion. At particular internuclear distances between the Rydberg atom and the ion, potential wells occur that can hold atom–ion molecular bound states. Apart from the binding mechanism, we describe important properties of the long-range atom–ion Rydberg molecule, such as its lifetime and decay paths, its vibrational and rotational structure, and its large dipole moment. Furthermore, we discuss methods of how to produce and detect it. The unusual properties of the long-range atom–ion Rydberg molecule give rise to interesting prospects for studies of wave packet dynamics in engineered potential energy landscapes. Full article

(This article belongs to the Special Issue Low Energy Interactions between Ions and Ultracold Alkali Atoms)

► Show Figures

Figure 1

13 pages, 2159 KiB

Open AccessEditor’s ChoiceArticle

Few Body Effects in the Electron and Positron Impact Ionization of Atoms

by R.I. Campeanu and Colm T. Whelan

Atoms 2021, 9(2), 33; https://doi.org/10.3390/atoms9020033 - 9 Jun 2021

Cited by 6 | Viewed by 2643

Abstract

Triple differential cross sections (TDCS) are presented for the electron and positron impact ionization of inert gas atoms in a range of energy sharing geometries where a number of significant few body effects compete to define the shape of the TDCS. Using both [...] Read more.

Triple differential cross sections (TDCS) are presented for the electron and positron impact ionization of inert gas atoms in a range of energy sharing geometries where a number of significant few body effects compete to define the shape of the TDCS. Using both positrons and electrons as projectiles has opened up the possibility of performing complementary studies which could effectively isolate competing interactions that cannot be separately detected in an experiment with a single projectile. Results will be presented in kinematics where the electron impact ionization appears to be well understood and using the same kinematics positron cross sections will be presented. The kinematics are then varied in order to focus on the role of distortion, post collision interaction (pci), and interference effects. Full article

(This article belongs to the Special Issue Electron Scattering in Gases –from Cross Sections to Plasma Modeling)

► Show Figures

Figure 1

8 pages, 273 KiB

Open AccessArticle

Electron-Impact Ionization of Heavy Atoms Using the Time-Dependent Close-Coupling Method

by Michael S. Pindzola, Stuart D. Loch and James P. Colgan

Atoms 2021, 9(2), 32; https://doi.org/10.3390/atoms9020032 - 8 Jun 2021

Cited by 1 | Viewed by 2242

Abstract

The time-dependent close-coupling method has been recently applied to calculate electron-impact direct ionization cross sections for the Kr, W, and Pb atoms. An overview is presented for these three heavy neutral atom systems. When the direct ionization cross sections are combined with excitation-autoionization [...] Read more.

The time-dependent close-coupling method has been recently applied to calculate electron-impact direct ionization cross sections for the Kr, W, and Pb atoms. An overview is presented for these three heavy neutral atom systems. When the direct ionization cross sections are combined with excitation-autoionization cross sections, the total ionization cross sections were found to be in reasonable agreement with crossed-beams measurements for Kr and Pb. Full article

► Show Figures

Figure 1

13 pages, 1753 KiB

Open AccessArticle

Calculation of Electron Impact Single Ionization TDCS of Tungsten Atoms at 200, 500 and 1000 eV

by Ghanshyam Purohit

Atoms 2021, 9(2), 31; https://doi.org/10.3390/atoms9020031 - 7 Jun 2021

Cited by 2 | Viewed by 2192

Abstract

We report triple differential cross-sections (TDCSs) for the electron impact single ionization of tungsten atoms for the ionization taking place from the outer sub shells of tungsten atoms, viz. W (6s), W (5d), W (5p) and W (4f). The study of the electron-induced [...] Read more.

We report triple differential cross-sections (TDCSs) for the electron impact single ionization of tungsten atoms for the ionization taking place from the outer sub shells of tungsten atoms, viz. W (6s), W (5d), W (5p) and W (4f). The study of the electron-induced processes such as ionization, excitation, autoionization from tungsten and its charged states is strongly required to diagnose and model the fusion plasma in magnetic devices such as Tokamaks. Particularly, the cross-section data are important to understand the electron spectroscopy involved in the fusion plasma. In the present study, we report TDCS results for the ionization of W atoms at 200, 500 and 1000 eV projectile energy at different values of scattered electron angles. It was observed that the trends of TDCSs for W (5d) are significantly different from the trends of TDCSs for W (6s), W (5p) and W (4f). It was further observed that the TDCS for W atoms has sensitive dependence on value of momentum transfer and projectile energy. Full article

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

► Show Figures

Figure 1

15 pages, 298 KiB

Open AccessArticle

Methods for Line Shapes in Plasmas in the Presence of External Electric Fields

by Spiros Alexiou

Atoms 2021, 9(2), 30; https://doi.org/10.3390/atoms9020030 - 26 May 2021

Cited by 4 | Viewed by 1905

Abstract

Line broadening is usually dominated by interactions of an atomic system with a stochastic, random medium. When, in addition to the random medium, a non-random field (such as a laser) is applied, the line profile may be modified in significant ways. The present [...] Read more.

Line broadening is usually dominated by interactions of an atomic system with a stochastic, random medium. When, in addition to the random medium, a non-random field (such as a laser) is applied, the line profile may be modified in significant ways. The present work discusses these modifications and the methods to deal with them. Full article

(This article belongs to the Special Issue The 5th Spectral Line Shapes Workshop: Current Topics in Spectral Line Broadening in Plasmas)

► Show Figures

Figure 1

8 pages, 259 KiB

Open AccessArticle

The Semiclassical Limit of the Gailitis Formula Applied to Electron Impact Broadening of Spectral Lines of Ionized Atoms

by Sylvie Sahal-Bréchot

Atoms 2021, 9(2), 29; https://doi.org/10.3390/atoms9020029 - 18 May 2021

Cited by 16 | Viewed by 1951

Abstract

The present paper revisits the determination of the semi-classical limit of the Feshbach resonances which play a role in electron impact broadening (the so-called “Stark“ broadening) of isolated spectral lines of ionized atoms. The Gailitis approximation will be used. A few examples of [...] Read more.

The present paper revisits the determination of the semi-classical limit of the Feshbach resonances which play a role in electron impact broadening (the so-called “Stark“ broadening) of isolated spectral lines of ionized atoms. The Gailitis approximation will be used. A few examples of results will be provided, showing the importance of the role of the Feshbach resonances. Full article

(This article belongs to the Special Issue The 5th Spectral Line Shapes Workshop: Current Topics in Spectral Line Broadening in Plasmas)

32 pages, 903 KiB

Open AccessEditor’s ChoiceReview

A Review of High-Gain Free-Electron Laser Theory

by Nicola Piovella and Luca Volpe

Atoms 2021, 9(2), 28; https://doi.org/10.3390/atoms9020028 - 12 May 2021

Cited by 9 | Viewed by 3358

Abstract

High-gain free-electron lasers, conceived in the 1980s, are nowadays the only bright sources of coherent X-ray radiation available. In this article, we review the theory developed by R. Bonifacio and coworkers, who have been some of the first scientists envisaging its operation as [...] Read more.

High-gain free-electron lasers, conceived in the 1980s, are nowadays the only bright sources of coherent X-ray radiation available. In this article, we review the theory developed by R. Bonifacio and coworkers, who have been some of the first scientists envisaging its operation as a single-pass amplifier starting from incoherent undulator radiation, in the so called self-amplified spontaneous emission (SASE) regime. We review the FEL theory, discussing how the FEL parameters emerge from it, which are fundamental for describing, designing and understanding all FEL experiments in the high-gain, single-pass operation. Full article

(This article belongs to the Special Issue Collective Atomic and Free-Electron Lasing)

► Show Figures

Figure 1

18 pages, 2416 KiB

Open AccessArticle

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

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

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

Cited by 4 | Viewed by 3134

Abstract

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

High-resolution K-shell photoionization cross-sections for the C-like atomic nitrogen ion (N⁺) are reported in the 398 eV (31.15 Å) to 450 eV (27.55 Å) energy (wavelength) range. The results were obtained from absolute ion-yield measurements using the SOLEIL synchrotron radiation facility for spectral bandpasses of 65 meV or 250 meV. In the photon energy region 398–403 eV,

1 s ⟶ 2 p

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

1 s ⟶ (1 s 2 s^{2} 2 p^{2 4} P) n p

and

1 s ⟶ (1 s 2 s^{2} 2 p^{2 2} P) n p

resonances forming well-developed Rydberg series up

n = 7 and n = 8

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

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

► Show Figures

Figure 1

12 pages, 335 KiB

Open AccessArticle

Relativistic Coupled-Cluster Calculations of Isotope Shifts for the Low-Lying States of Ca II in the Finite-Field Approach

by Anaïs Dorne, Bijaya K. Sahoo and Anders Kastberg

Atoms 2021, 9(2), 26; https://doi.org/10.3390/atoms9020026 - 3 May 2021

Cited by 4 | Viewed by 2376

Abstract

We have evaluated the isotope shift (IS) constants of the first five low-lying fine-structure states of the singly charged calcium ion (Ca II) by adopting a finite-field (FF) approach in the relativistic coupled-cluster (RCC), a method developed by us and by using a [...] Read more.

We have evaluated the isotope shift (IS) constants of the first five low-lying fine-structure states of the singly charged calcium ion (Ca II) by adopting a finite-field (FF) approach in the relativistic coupled-cluster (RCC), a method developed by us and by using a code also developed by us. A similar previous calculation using singles and doubles approximation RCC theory (RCCSD method), gives results for the individual states in the FF approach that deviate substantially, while the differential values (the shifts of the spectral lines) agree reasonably well with other theoretical results and with experiments. However, we find a contrasting trend from the FF approach using our RCCSD method although calculations with the Dirac–Hartree–Fock (DHF) method shows good agreement. Our results also show that inclusion of partial triple excitations in the perturbative approach (RCCSD(T) method) through energy derivation lessens accuracy, but these results can be improved when triple excitations are included in the wave function that determines the RCC equations. The differences between the RCCSD and RCCSD(T) results demonstrate the importance of triple excitations in evaluating energies and IS constants for Ca II. Finally, we also present ab initio values of IS’s between the S–P, S–D, and D–P transitions in the DHF, and RCCSD and RCCSD(T) approximations and this is compared to the previously reported values (theoretical as well as experimental). Full article

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

► Show Figures

Figure 1

12 pages, 4200 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Route to Extend the Lifetime of a Discrete Time Crystal in a Finite Spin Chain without Disorder

by Sayan Choudhury

Atoms 2021, 9(2), 25; https://doi.org/10.3390/atoms9020025 - 12 Apr 2021

Cited by 4 | Viewed by 3344

Abstract

Periodically driven (Floquet) systems are described by time-dependent Hamiltonians that possess discrete time translation symmetry. The spontaneous breaking of this symmetry leads to the emergence of a novel non-equilibrium phase of matter—the Discrete Time Crystal (DTC). In this paper, we propose a scheme [...] Read more.

Periodically driven (Floquet) systems are described by time-dependent Hamiltonians that possess discrete time translation symmetry. The spontaneous breaking of this symmetry leads to the emergence of a novel non-equilibrium phase of matter—the Discrete Time Crystal (DTC). In this paper, we propose a scheme to extend the lifetime of a DTC in a paradigmatic model—a translation-invariant Ising spin chain with nearest-neighbor interaction J, subjected to a periodic kick by a transverse magnetic field with frequency

\frac{2 π}{T}

. This system exhibits the hallmark signature of a DTC—persistent sub-harmonic oscillations with frequency

\frac{π}{T}

—for a wide parameter regime. Employing both analytical arguments as well as exact diagonalization calculations, we demonstrate that the lifetime of the DTC is maximized, when the interaction strength is tuned to an optimal value,

J T = π

. Our proposal essentially relies on an interaction-induced quantum interference mechanism that suppresses the creation of excitations, and thereby enhances the DTC lifetime. Intriguingly, we find that the period doubling oscillations can last eternally in even size systems. This anomalously long lifetime can be attributed to a time reflection symmetry that emerges at

J T = π

. Our work provides a promising avenue for realizing a robust DTC in various quantum emulator platforms. Full article

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

► Show Figures

Figure 1

14 pages, 8961 KiB

Open AccessEditor’s ChoiceArticle

CAl₄Mg^0/−: Global Minima with a Planar Tetracoordinate Carbon Atom

by Nisha Job, Maya Khatun, Krishnan Thirumoorthy, Sasanka Sankhar Reddy CH, Vijayanand Chandrasekaran, Anakuthil Anoop and Venkatesan S. Thimmakondu

Atoms 2021, 9(2), 24; https://doi.org/10.3390/atoms9020024 - 9 Apr 2021

Cited by 18 | Viewed by 5399

Abstract

Isomers of CAl₄Mg and CAl₄Mg⁻ have been theoretically characterized for the first time. The most stable isomer for both the neutral and anion contain a planar tetracoordinate carbon (ptC) atom. Unlike the isovalent CAl₄Be case, which [...] Read more.

Isomers of CAl₄Mg and CAl₄Mg⁻ have been theoretically characterized for the first time. The most stable isomer for both the neutral and anion contain a planar tetracoordinate carbon (ptC) atom. Unlike the isovalent CAl₄Be case, which contains a planar pentacoordinate carbon atom as the global minimum geometry, replacing beryllium with magnesium makes the ptC isomer the global minimum due to increased ionic radii of magnesium. However, it is relatively easier to conduct experimental studies for CAl₄Mg^0/− as beryllium is toxic. While the neutral molecule containing the ptC atom follows the 18 valence electron rule, the anion breaks the rule with 19 valence electrons. The electron affinity of CAl₄Mg is in the range of 1.96–2.05 eV. Both the global minima exhibit π/σ double aromaticity. Ab initio molecular dynamics simulations were carried out for both the global minima at 298 K for 10 ps to confirm their kinetic stability. Full article

(This article belongs to the Special Issue Planar Tetracoordinate Carbon—Fifty Years and Beyond)

► Show Figures

Figure 1

41 pages, 877 KiB

Open AccessArticle

EUV Beam-Foil Spectra of Scandium, Vanadium, Chromium, Manganese, Cobalt, and Zinc

by Elmar Träbert

Atoms 2021, 9(2), 23; https://doi.org/10.3390/atoms9020023 - 29 Mar 2021

Cited by 3 | Viewed by 3115

Abstract

Beam-foil extreme-ultraviolet spectra of Sc, V, Cr, Mn, Co and Zn are presented that provide survey data of a single element exclusively. Various details are discussed in the context of line intensity ratios, yrast transitions, delayed spectra and peculiar properties of the beam-foil [...] Read more.

Beam-foil extreme-ultraviolet spectra of Sc, V, Cr, Mn, Co and Zn are presented that provide survey data of a single element exclusively. Various details are discussed in the context of line intensity ratios, yrast transitions, delayed spectra and peculiar properties of the beam-foil light source. Full article

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

► Show Figures

Figure 1

9 pages, 396 KiB

Open AccessArticle

Initial Dynamics of Quantum Impurities in a Bose–Einstein Condensate

by Magnus G. Skou, Thomas G. Skov, Nils B. Jørgensen and Jan J. Arlt

Atoms 2021, 9(2), 22; https://doi.org/10.3390/atoms9020022 - 27 Mar 2021

Cited by 5 | Viewed by 2651

Abstract

An impurity immersed in a medium constitutes a canonical scenario applicable in a wide range of fields in physics. Though our understanding has advanced significantly in the past decades, quantum impurities in a bosonic environment are still of considerable theoretical and experimental interest. [...] Read more.

An impurity immersed in a medium constitutes a canonical scenario applicable in a wide range of fields in physics. Though our understanding has advanced significantly in the past decades, quantum impurities in a bosonic environment are still of considerable theoretical and experimental interest. Here, we discuss the initial dynamics of such impurities, which was recently observed in interferometric experiments. Experimental observations from weak to unitary interactions are presented and compared to a theoretical description. In particular, the transition between two initial dynamical regimes dominated by two-body interactions is analyzed, yielding transition times in clear agreement with the theoretical prediction. Additionally, the distinct time dependence of the coherence amplitude in these regimes is obtained by extracting its power-law exponents. This benchmarks our understanding and suggests new ways of probing dynamical properties of quantum impurities. Full article

(This article belongs to the Special Issue Physics of Impurities in Quantum Gases)

► Show Figures

Figure 1

12 pages, 349 KiB

Open AccessArticle

Semiclassical Phase Analysis for a Trapped-Atom Sagnac Interferometer

by Zhe Luo, E. R. Moan and C. A. Sackett

Atoms 2021, 9(2), 21; https://doi.org/10.3390/atoms9020021 - 27 Mar 2021

Cited by 1 | Viewed by 2624

Abstract

A Sagnac atom interferometer can be constructed using a Bose–Einstein condensate trapped in a cylindrically symmetric harmonic potential. Using the Bragg interaction with a set of laser beams, the atoms can be launched into circular orbits, with two counterpropagating interferometers allowing many sources [...] Read more.

A Sagnac atom interferometer can be constructed using a Bose–Einstein condensate trapped in a cylindrically symmetric harmonic potential. Using the Bragg interaction with a set of laser beams, the atoms can be launched into circular orbits, with two counterpropagating interferometers allowing many sources of common-mode noise to be excluded. In a perfectly symmetric and harmonic potential, the interferometer output would depend only on the rotation rate of the apparatus. However, deviations from the ideal case can lead to spurious phase shifts. These phase shifts have been theoretically analyzed for anharmonic perturbations up to quartic in the confining potential, as well as angular deviations of the laser beams, timing deviations of the laser pulses, and motional excitations of the initial condensate. Analytical and numerical results show the leading effects of the perturbations to be second order. The scaling of the phase shifts with the number of orbits and the trap axial frequency ratio are determined. The results indicate that sensitive parameters should be controlled at the

10^{- 5}

level to accommodate a rotation sensing accuracy of

10^{- 9}

rad/s. The leading-order perturbations are suppressed in the case of perfect cylindrical symmetry, even in the presence of anharmonicity and other errors. An experimental measurement of one of the perturbation terms is presented. Full article

(This article belongs to the Special Issue Atomic Interferometry with Bose–Einstein Condensates)

► Show Figures

Figure 1

11 pages, 397 KiB

Open AccessArticle

Angular Distribution of Characteristic Radiation Following the Excitation of He-Like Uranium in Relativistic Collisions

by Alexandre Gumberidze, Daniel B. Thorn, Andrey Surzhykov, Christopher J. Fontes, Dariusz Banaś, Heinrich F. Beyer, Weidong Chen, Robert E. Grisenti, Siegbert Hagmann, Regina Hess, Pierre-Michel Hillenbrand, Paul Indelicato, Christophor Kozhuharov, Michael Lestinsky, Renate Märtin, Nikolaos Petridis, Roman V. Popov, Reinhold Schuch, Uwe Spillmann, Stanislav Tashenov, Sergiy Trotsenko, Andrzej Warczak, Günter Weber, Weiqiang Wen, Danyal F. A. Winters, Natalya Winters, Zhong Yin and Thomas Stöhlker Show full author list Hide full author list

Atoms 2021, 9(2), 20; https://doi.org/10.3390/atoms9020020 - 25 Mar 2021

Cited by 4 | Viewed by 3635

Abstract

In this paper, we present an experimental and theoretical study of excitation processes for the heaviest stable helium-like ion, that is, He-like uranium occurring in relativistic collisions with hydrogen and argon targets. In particular, we concentrate on angular distributions of the characteristic K [...] Read more.

In this paper, we present an experimental and theoretical study of excitation processes for the heaviest stable helium-like ion, that is, He-like uranium occurring in relativistic collisions with hydrogen and argon targets. In particular, we concentrate on angular distributions of the characteristic K

α

radiation following the K → L excitation of He-like uranium. We pay special attention to the magnetic sub-level population of the excited

1 s 2 l_{j}

states, which is directly related to the angular distribution of the characteristic K

α

radiation. We show that the experimental data can be well described by calculations taking into account the excitation by the target nucleus as well as by the target electrons. Moreover, we demonstrate for the first time an important influence of the electron-impact excitation process on the angular distributions of the K

α

radiation produced by excitation of He-like uranium in collisions with different targets. Full article

(This article belongs to the Special Issue Accelerator-Based Atomic Physics: Fast Ion–Atom and Ion–Molecule Collisions)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Atoms, Volume 9, Issue 2 (June 2021) – 15 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI