Atoms

12 pages, 1059 KiB

Open AccessArticle

Fourier-Transform VUV Spectroscopy of ^14,15N and ^12,13C

by Kin-Fung Lai, Wim Ubachs, Nelson De Oliveira and Edcel J. Salumbides

Atoms 2020, 8(3), 62; https://doi.org/10.3390/atoms8030062 - 22 Sep 2020

Cited by 5 | Viewed by 2593

Accurate Fourier-transform spectroscopic absorption measurements of vacuum ultraviolet transitions in atomic nitrogen and carbon were performed at the Soleil synchrotron. For

^{14}

N, transitions from the

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

S

_{3 / 2}

ground state and from the [...] Read more.

Accurate Fourier-transform spectroscopic absorption measurements of vacuum ultraviolet transitions in atomic nitrogen and carbon were performed at the Soleil synchrotron. For

^{14}

N, transitions from the

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

S

_{3 / 2}

ground state and from the

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

P and

^{2}

D metastable states were determined in the 95–124 nm range at an accuracy of

0.025 {cm}^{- 1}

. The combination of these results with data from previous precision laser experiments in the vacuum ultraviolet range reveals an overall and consistent offset of −0.04 cm

^{- 1}

from values reported in the NIST database. The splittings of the

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

S

_{3 / 2}

–

2 s 2 p^{4}^{4}

P

_{J}

transitions are well-resolved for

^{14}

N and

^{15}

N and the isotope shifts determined. While excitation of a

2 p

valence electron yields very small isotope shifts, excitation of a

2 s

core electron results in large isotope shifts, in agreement with theoretical predictions. For carbon, six transitions from the ground

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

P

_{J}

and

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

P

_{J}

excited states at 165 nm are measured for both

^{12}

C and

^{13}

C isotopes. Full article

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

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21 pages, 789 KiB

Open AccessArticle

Radiative Cascade Repopulation of 1s2s2p ⁴P States Formed by Single Electron Capture in 2–18 MeV Collisions of C⁴⁺ (1s2s ³S) with He

by Theo J. M. Zouros, Sofoklis Nikolaou, Ioannis Madesis, Angelos Laoutaris, Stefanos Nanos, Alain Dubois and Emmanouil P. Benis

Atoms 2020, 8(3), 61; https://doi.org/10.3390/atoms8030061 - 21 Sep 2020

Cited by 3 | Viewed by 2753

Abstract

This study focuses on the details of cascade repopulation of doubly excited triply open-shell C

^{3 +} (1 s 2 s 2 p)

^{4} P

and

^{2} P_{\pm}

states produced in 2–18 MeV collisions of C [...] Read more.

This study focuses on the details of cascade repopulation of doubly excited triply open-shell C

^{3 +} (1 s 2 s 2 p)

^{4} P

and

^{2} P_{\pm}

states produced in 2–18 MeV collisions of C

^{4 +} (1 s 2 s^{3} S)

with He. Such cascade calculations are necessary for the correct determination of the ratio R of their cross sections, used as a measure of spin statistics [Madesis et al. PRL 124 (2020) 113401]. Here, we present the details of our cascade calculations within a new matrix formulation based on the well-known diagrammatic cascade approach [Curtis, Am. J. Phys. 36 (1968) 1123], extended to also include Auger depopulation. The initial populations of the

1 s 2 s n ℓ^{4} L

and

1 s 2 s n ℓ^{2} L

levels included in our analysis are obtained from the direct

n ℓ

single electron capture (SEC) cross sections, calculated using the novel three-electron close-coupling (3eAOCC) approach. All relevant radiative branching ratios (RBR) for

n \leq 4

were computed using the COWAN code. While doublet RBRs are found to be very small, quartet RBRs are found to be large, indicating cascade feeding to be important only for quartets, consistent with previous findings. Calculations including up to third order cascades, extended to

n \to \infty

using an

n^{- 3}

SEC model, showed a ∼60% increase of the

1 s 2 s 2 p^{4} P

populations due to cascades, resulting, for the first time, in R values in good overall agreement with experiment. Full article

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

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9 pages, 388 KiB

Open AccessArticle

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

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

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

Cited by 1 | Viewed by 2494

Abstract

Inner-shell photodetachment of Na

^{-}

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

Inner-shell photodetachment of Na

^{-}

near the L-edge threshold was investigated using the R-matrix method. Significant structure was found in the cross section, and this structure is shown to be related to the complicated correlated electron dynamics endemic in negative ions. Comparison with experiment suggests that the absolute values of the measured cross section might be too small by a factor of two. Full article

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

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14 pages, 1072 KiB

Open AccessEditor’s ChoiceArticle

Net Electron Capture in Collisions of Multiply Charged Projectiles with Biologically Relevant Molecules

by Hans Jürgen Lüdde, Alba Jorge, Marko Horbatsch and Tom Kirchner

Atoms 2020, 8(3), 59; https://doi.org/10.3390/atoms8030059 - 17 Sep 2020

Cited by 10 | Viewed by 2834

Abstract

A model for the description of proton collisions from molecules composed of atoms such as hydrogen, carbon, nitrogen, oxygen and phosphorus (H, C, N, O, P) was recently extended to treat collisions with multiply charged ions with a focus on net ionization. Here [...] Read more.

A model for the description of proton collisions from molecules composed of atoms such as hydrogen, carbon, nitrogen, oxygen and phosphorus (H, C, N, O, P) was recently extended to treat collisions with multiply charged ions with a focus on net ionization. Here we complement the work by focusing on net capture. The ion–atom collisions are computed using the two-center basis generator method. The atomic net capture cross sections are then used to assemble two models for ion–molecule collisions: An independent atom model (IAM) based on the Bragg additivity rule (labeled IAM-AR), and also the so-called pixel-counting method (IAM-PCM) which introduces dependence on the orientation of the molecule during impact. The IAM-PCM leads to significantly reduced capture cross sections relative to IAM-AR at low energies, since it takes into account the overlap of effective atomic cross sectional areas. We compare our results with available experimental and other theoretical data focusing on water vapor (

H_{2} O

), methane (

{CH}_{4}

) and uracil (

C_{4} H_{4} N_{2} O_{2}

). For the water molecule target we also provide results from a classical-trajectory Monte Carlo approach that includes dynamical screening effects on projectile and target. For small molecules dominated by a many-electron atom, such as carbon in methane or oxygen in water, we find a saturation phenomenon for higher projectile charges (

q = 3

) and low energies, where the net capture cross section for the molecule is dominated by the net cross section for the many-electron atom, and the net capture cross section is not proportional to the total number of valence electrons. Full article

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

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8 pages, 306 KiB

Open AccessArticle

Phase Diagram of the Attractive Kane-Mele-Hubbard Model at Half Filling

by Zlatko Koinov

Atoms 2020, 8(3), 58; https://doi.org/10.3390/atoms8030058 - 14 Sep 2020

Viewed by 2533

Abstract

Motivated by recent developments in the experimental study of ultracold atoms in graphene-like honeycomb optical lattices, we investigate superconductivity of the attractive Kane-Mele-Habbard (KMH) model with the next-nearest-neighbor (NNN) hoping at half filling. The mean-field approximation is used to study the phase diagram [...] Read more.

Motivated by recent developments in the experimental study of ultracold atoms in graphene-like honeycomb optical lattices, we investigate superconductivity of the attractive Kane-Mele-Habbard (KMH) model with the next-nearest-neighbor (NNN) hoping at half filling. The mean-field approximation is used to study the phase diagram which interpolates the trivial and the non-trivial topological states. It is shown that: (a) when the NNN hoping is taken into account, one has to introduce two mean-field gap equations for the two sublattices, instead of a single gap when the NNN hopping is neglected, and (b) in the non-trivial topological region the phase diagram with the NNN hopping is significantly different compared to the phase diagram calculated previously, but without the NNN term. We also discuss the superconducting instability of the attractive KMH model that is driven by condensation of Cooperons. Full article

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

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16 pages, 811 KiB

Open AccessArticle

Rayleigh and Raman Scattering from Alkali Atoms

by Adam Singor, Dmitry Fursa, Keegan McNamara and Igor Bray

Atoms 2020, 8(3), 57; https://doi.org/10.3390/atoms8030057 - 7 Sep 2020

Cited by 3 | Viewed by 2945

Abstract

Two computational methods developed recently [McNamara, Fursa, and Bray, Phys. Rev. A 98, 043435 (2018)] for calculating Rayleigh and Raman scattering cross sections for atomic hydrogen have been extended to quasi one-electron systems. A comprehensive set of cross sections have been obtained [...] Read more.

Two computational methods developed recently [McNamara, Fursa, and Bray, Phys. Rev. A 98, 043435 (2018)] for calculating Rayleigh and Raman scattering cross sections for atomic hydrogen have been extended to quasi one-electron systems. A comprehensive set of cross sections have been obtained for the alkali atoms: lithium, sodium, potassium, rubidium, and cesium. These cross sections are accurate for incident photon energies above and below the ionization threshold, but they are limited to energies below the excitation threshold of core electrons. The effect of spin-orbit interaction, importance of accounting for core polarization, and convergence of the cross sections have been investigated. Full article

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

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11 pages, 4320 KiB

Open AccessEditor’s ChoiceArticle

Development of NIST Atomic Databases and Online Tools

by Yuri Ralchenko and Alexander Kramida

Atoms 2020, 8(3), 56; https://doi.org/10.3390/atoms8030056 - 5 Sep 2020

Cited by 186 | Viewed by 7026

Abstract

Over the last 25 years, the atomic standard reference databases and online tools developed at the National Institute of Standards and Technology (NIST) have provided users around the world with the highest-quality data on various atomic parameters (e.g., level energies, transition wavelengths, and [...] Read more.

Over the last 25 years, the atomic standard reference databases and online tools developed at the National Institute of Standards and Technology (NIST) have provided users around the world with the highest-quality data on various atomic parameters (e.g., level energies, transition wavelengths, and oscillator strengths) and online capabilities for fast and reliable collisional-radiative modeling of diverse plasmas. Here we present an overview of the recent developments regarding NIST numerical and bibliographic atomic databases and outline the prospects and vision of their evolution. Full article

(This article belongs to the Special Issue Development and Perspectives of Atomic and Molecular Databases)

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8 pages, 1063 KiB

Open AccessArticle

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

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

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

Cited by 2 | Viewed by 2811

Abstract

The photoabsorption spectrum of Bi⁺ was measured in the wavelength range between 37 and 60 nm, using the dual laser plasma technique in which one plasma is used as the source of vacuum ultraviolet continuum radiation and the other plasma is used [...] Read more.

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

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

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10 pages, 568 KiB

Open AccessArticle

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

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

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

Cited by 4 | Viewed by 2664

Abstract

Photoelectron angular distributions of the two-photon ionization of neutral atoms are theoretically investigated. Numerical calculations of two-photon ionization cross sections and asymmetry parameters are carried out within the independent-particle approximation and relativistic second-order perturbation theory. The dependence of the asymmetry parameters on the [...] Read more.

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

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

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19 pages, 328 KiB

Open AccessArticle

Reducing a Class of Two-Dimensional Integrals to One-Dimension with an Application to Gaussian Transforms

by Jack C. Straton

Atoms 2020, 8(3), 53; https://doi.org/10.3390/atoms8030053 - 2 Sep 2020

Viewed by 1899

Abstract

Quantum theory is awash in multidimensional integrals that contain exponentials in the integration variables, their inverses, and inverse polynomials of those variables. The present paper introduces a means to reduce pairs of such integrals to one dimension when the integrand contains powers multiplied [...] Read more.

Quantum theory is awash in multidimensional integrals that contain exponentials in the integration variables, their inverses, and inverse polynomials of those variables. The present paper introduces a means to reduce pairs of such integrals to one dimension when the integrand contains powers multiplied by an arbitrary function of

x y / (x + y)

multiplying various combinations of exponentials. In some cases these exponentials arise directly from transition-amplitudes involving products of plane waves, hydrogenic wave functions, and Yukawa and/or Coulomb potentials. In other cases these exponentials arise from Gaussian transforms of such functions. Full article

14 pages, 434 KiB

Open AccessArticle

Investigation of a Collisional Radiative Model for Laser-Produced Plasmas

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

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

Cited by 5 | Viewed by 3289 | Correction

Abstract

Plasmas of a variety of types can be described by the collisional radiative (CR) model developed by Colombant and Tonan. From the CR model, the ion distribution of a plasma at a given electron temperature and density can be found. This information is [...] Read more.

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

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

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14 pages, 4235 KiB

Open AccessArticle

Partial Photoionization Cross Sections of Chromium from the Ground and Excited States

by Oleg Zatsarinny and Swaraj Tayal

Atoms 2020, 8(3), 51; https://doi.org/10.3390/atoms8030051 - 27 Aug 2020

Cited by 3 | Viewed by 2721

Abstract

Partial and total photoionization cross sections of iron-peak elements are important for the determination of abundances in late-type stars and nebular objects. We have investigated photoionization of neutral chromium from the ground and excited states in the low energy region from the first [...] Read more.

Partial and total photoionization cross sections of iron-peak elements are important for the determination of abundances in late-type stars and nebular objects. We have investigated photoionization of neutral chromium from the ground and excited states in the low energy region from the first ionization threshold at 6.77 eV to 30 eV. Accurate descriptions of the initial bound states of Cr I and the final residual Cr II ionic states have been obtained in the multiconfiguration Hartree-Fock method together with adjustable configuration expansions and term-dependent non-orthogonal orbitals. The B-spline R-matrix method has been used for the calculation of photoionization cross sections. The 194

L S

final ionic states of Cr II

3 d^{4} 4 s

,

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

,

3 d^{5}

,

3 d^{4} 4 p

, and

3 d^{3} 4 s 4 p

principal configurations have been included in the close-coupling expansion. The inclusion of all terms of these configurations has significant impact on the near-threshold resonance structures as well as on the nonresonant background cross sections. Total photoionization cross sections from the ground

3 d^{5} 4 s

a^{7} S

and excited

3 d^{5} 4 s

a^{5} S

,

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

a^{5} D

,

3 d^{5} 4 p

z^{5} P

, and

3 d^{4} 4 s 4 p

y^{5} P

states of Cr I have been compared with other available R-matrix calculation to estimate the likely uncertainties in photoionization cross sections. We analyzed the partial photoionization cross sections for leaving the residual ion in various states to identify the important scattering channels, and noted that

3 d

electron ionization channel becomes dominant at higher energies. Full article

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15 pages, 2143 KiB

Open AccessArticle

Plasma Temperature and Electron Density Determination Using Laser-Induced Breakdown Spectroscopy (LIBS) in Earth’s and Mars’s Atmospheres

by Julian Stetzler, Shijun Tang and Rosemarie C. Chinni

Atoms 2020, 8(3), 50; https://doi.org/10.3390/atoms8030050 - 25 Aug 2020

Cited by 12 | Viewed by 4109

Abstract

The purpose of this study was to calculate and compare the plasma temperatures and electron densities from the laser-induced breakdown spectroscopy (LIBS) data collected by NASA’s Martian rover and compare them to samples measured in Earth’s atmosphere. Using the Boltzmann plots, LIBS plasma [...] Read more.

The purpose of this study was to calculate and compare the plasma temperatures and electron densities from the laser-induced breakdown spectroscopy (LIBS) data collected by NASA’s Martian rover and compare them to samples measured in Earth’s atmosphere. Using the Boltzmann plots, LIBS plasma temperatures were obtained for each site. The analysis focused on titanium lines that were located in the spectral region between 300 and 310 nm. The electron density was measured using the Stark broadening of the hydrogen line at 656.6 nm; the full width at half maximum (FWHM) of this line can be measured and correlated to the electron density of the plasma. Due to a neighboring carbon peak with the hydrogen line seen in many of the spectra from the Martian sites, the FWHM needed to be calculated using a computer program that completed the other side of the hydrogen line and then it calculated the FWHM for those data samples affected by this. The plasma temperatures and electron densities of the Martian sites were compared to LIBS samples taken on Earth. Full article

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20 pages, 772 KiB

Open AccessEditor’s ChoiceArticle

PyAtomDB: Extending the AtomDB Atomic Database to Model New Plasma Processes and Uncertainties

by Adam R. Foster and Keri Heuer

Atoms 2020, 8(3), 49; https://doi.org/10.3390/atoms8030049 - 24 Aug 2020

Cited by 32 | Viewed by 3617

Abstract

The AtomDB project provides models of X-ray and extreme ultraviolet emitting astrophysical spectra for optically thin, hot plasma. We present the new software package, PyAtomDB, which now underpins the entire project, providing access to the underlying database, collisional radiative model calculations, and spectrum [...] Read more.

The AtomDB project provides models of X-ray and extreme ultraviolet emitting astrophysical spectra for optically thin, hot plasma. We present the new software package, PyAtomDB, which now underpins the entire project, providing access to the underlying database, collisional radiative model calculations, and spectrum generation for a range of models. PyAtomDB is easily extensible, allowing users to build new tools and models for use in analysis packages such as XSPEC. We present two of these, the kappa and ACX models for non-Maxwellian and Charge-Exchange plasmas respectively. In addition, PyAtomDB allows for full open access to the apec code, which underlies all of the AtomDB spectra and has enabled the development of a module for estimating the sensitivity of emission lines and diagnostic line ratios to uncertainties in the underlying atomic data. We present these publicly available tools and results for several X-ray diagnostics of Fe L-shell ions and He-like ions as examples. Full article

(This article belongs to the Special Issue Development and Perspectives of Atomic and Molecular Databases)

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26 pages, 7350 KiB

Open AccessArticle

Simulations of Ion-Guiding Through Insulating Nanocapillaries of Varying Diameter: Interpretation of Experimental Results

by Nikolaus Stolterfoht

Atoms 2020, 8(3), 48; https://doi.org/10.3390/atoms8030048 - 21 Aug 2020

Cited by 6 | Viewed by 2632

Abstract

The guiding of highly charged ions through a single nanocapillary is simulated in comparison with previous experiments performed with highly insulating polyethylene terephthalate (PET). The simulations are carried out using 3-keV Ne

^{7 +}

ions injected into capillaries with diameters ranging from 100 [...] Read more.

The guiding of highly charged ions through a single nanocapillary is simulated in comparison with previous experiments performed with highly insulating polyethylene terephthalate (PET). The simulations are carried out using 3-keV Ne

^{7 +}

ions injected into capillaries with diameters ranging from 100 nm to 400 nm. In the calculations, non-linear effects are applied to model the charge transport along the capillary surface and into the bulk depleting the deposited charges from the capillary walls. In addition to the surface carrier mobility, the non-linear effects are also implemented into the bulk conductivity. A method is presented to determine the parameters of the surface charge transport and the bulk conductivity by reproducing the oscillatory structure of the mean emission angle. A common set of charge depletion rates are determined with relatively high accuracy providing confidence in the present theoretical analysis. Significant differences in the oscillatory structures, experimentally observed, are explained by the calculations. Experimental and theoretical results of the guiding power for capillaries of different diameters are compared. Finally, dynamic non-linear effects on the surface and bulk relaxation rates are determined from the simulations. Full article

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

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9 pages, 498 KiB

Open AccessArticle

Electric Field Excitation Suppression in Cold Atoms

by Jianing Han, Juliet Mitchell and Morgan Umstead

Atoms 2020, 8(3), 47; https://doi.org/10.3390/atoms8030047 - 20 Aug 2020

Viewed by 2142

Abstract

In this article, the atom excitation suppression is studied in two mechanisms. The first mechanism for excitation suppression is caused by an external DC electric field. The second mechanism is due to the energy shift caused by an electric field generated by free [...] Read more.

In this article, the atom excitation suppression is studied in two mechanisms. The first mechanism for excitation suppression is caused by an external DC electric field. The second mechanism is due to the energy shift caused by an electric field generated by free charges, which are created by ionizing atoms. The latter mechanism is known as the Coulomb blockade. Here, the Coulomb forces originate from ions created by ionizing atoms with a UV laser. The interaction, which causes the suppression, is treated theoretically as dipole–charge interactions. In the model, the charge is an ion, and the dipole is an atom. From measurements, we use

^{85}

Rb atoms. The valence electron and the ion core are the two poles of an electric dipole. The interaction potential energy between the ion and the atom is proportional to

\frac{1}{R^{2}}

, and the frequency shift caused by this interaction is proportional to

\frac{1}{R^{4}}

, where R is the distance between the ion and the dipole considered. This research is motivated by potential applications for quantum information storage, remote control, creating hot plasmas using cold atoms, as well as electronic devices. Full article

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16 pages, 353 KiB

Open AccessEditor’s ChoiceArticle

Atomic Data for Plasma Spectroscopy: The CHIANTI Database, Improvements and Challenges

by Giulio Del Zanna and Peter R. Young

Atoms 2020, 8(3), 46; https://doi.org/10.3390/atoms8030046 - 20 Aug 2020

Cited by 20 | Viewed by 3432

Abstract

CHIANTI is an atomic database and software package for modeling emission lines and continua from hot astrophysical plasmas. It is freely available to all researchers and has been widely used in the Heliophysics and Astrophysics communities for almost 25 years. In this review, [...] Read more.

CHIANTI is an atomic database and software package for modeling emission lines and continua from hot astrophysical plasmas. It is freely available to all researchers and has been widely used in the Heliophysics and Astrophysics communities for almost 25 years. In this review, we summarize the properties of the current version of the database and give an overview of the relevant atomic processes. We also discuss progress towards a complete implementation of collisional-radiative modeling, simultaneously solving for atomic level and ion populations for individual elements. Full article

(This article belongs to the Special Issue Development and Perspectives of Atomic and Molecular Databases)

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17 pages, 2879 KiB

Open AccessEditor’s ChoiceReview

Photoionization of Astrophysically Relevant Atomic Ions at PIPE

by Stefan Schippers and Alfred Müller

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

Cited by 11 | Viewed by 3169

Abstract

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

We review recent work on the photoionization of atomic ions of astrophysical interest that has been carried out at the photon-ion merged-beams setup PIPE, a permanently installed end station at the XUV beamline P04 of the PETRA III synchrotron radiation source operated by DESY in Hamburg, Germany. Our results on single and multiple L-shell photoionization of Fe

^{+}

, Fe

^{2 +}

, and Fe

^{3 +}

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

^{-}

, C

^{+}

, C

^{4 +}

, Ne

^{+}

, and Si

^{2 +}

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

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

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8 pages, 2754 KiB

Open AccessArticle

Spectroscopic Measurement of Hydrogen Atom Density in a Plasma Produced with 28 GHz ECH in QUEST

by Satoru Mori, Taiichi Shikama, Kazuaki Hanada, Nao Yoneda, Arseniy Kuzmin, Masahiro Hasuo, Hiroshi Idei, Takumi Onchi, Akira Ejiri, Yuki Osawa, Yi Peng, Kyohei Matsuzaki, Shinichiro Kado, Keiji Sawada, Takeshi Ido, Kazuo Nakamura, Ryuya Ikezoe, Yoshihiko Nagashima, Makoto Hasegawa, Kengo Kuroda, Aki Higashijima, Takahiro Nagata and Shun Shimabukuro Show full author list Hide full author list

Atoms 2020, 8(3), 44; https://doi.org/10.3390/atoms8030044 - 18 Aug 2020

Cited by 3 | Viewed by 2575

Abstract

The spatial distribution of the hydrogen atom density was evaluated in a spherical tokamak (ST) plasma sustained only with 28 GHz electron cyclotron heating (ECH). The radially resolved H_δ emissivity was measured using multiple viewing chord spectroscopy and Abel inversion. A collisional-radiative [...] Read more.

The spatial distribution of the hydrogen atom density was evaluated in a spherical tokamak (ST) plasma sustained only with 28 GHz electron cyclotron heating (ECH). The radially resolved H_δ emissivity was measured using multiple viewing chord spectroscopy and Abel inversion. A collisional-radiative (CR) model analysis of the emissivity resulted in a ground-state hydrogen atom density of 10¹⁵–10¹⁶ m⁻³ and an ionization degree of 1–0.85 in the plasma. Full article

(This article belongs to the Special Issue Atomic and Molecular Spectra in Magnetically Confined Torus Plasmas)

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3 pages, 15805 KiB

Open AccessEditorial

The 13th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas

by Jun Xiao, Tomas Brage and Roger Hutton

Atoms 2020, 8(3), 43; https://doi.org/10.3390/atoms8030043 - 11 Aug 2020

Viewed by 2109

Abstract

The 13th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas (ASOS2019), co-hosted by Fudan and Lund Universities, was held at Fudan University from 23–27 June 2019 [...] Full article

(This article belongs to the Special Issue 13th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas)

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10 pages, 1996 KiB

Open AccessArticle

Wave-Kinetic Approach to Collective Atomic Emission

by José Tito Mendonça and Antonio P. B. Serbêto

Atoms 2020, 8(3), 42; https://doi.org/10.3390/atoms8030042 - 10 Aug 2020

Cited by 3 | Viewed by 2077

Abstract

We study the collective scattering of radiation by a large ensemble of

N_{a} ≫ 1

atoms, in the presence of a pump field. We use the wave-kinetic approach where the center-of-mass position of the moving atoms is described by a microscopic discrete [...] Read more.

We study the collective scattering of radiation by a large ensemble of

N_{a} ≫ 1

atoms, in the presence of a pump field. We use the wave-kinetic approach where the center-of-mass position of the moving atoms is described by a microscopic discrete distribution, or alternatively, by a Wigner distribution. This approach can include thermal effects and quantum recoil in a natural way, and even consider atomic ensembles out of equilibrium. We assume two-level atoms with atomic transition frequency

ω_{a}

very different from the frequency

ω_{0}

of the pump field. We consider both the quasi-classical and quantum descriptions of the center-of-mass motion. In both cases, we establish the unstable regimes where coherent emission of radiation can take place. Full article

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

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7 pages, 1112 KiB

Open AccessArticle

Time Dependence of Ultra-Short Laser Pulses Scattering by Atom in High Frequency Limit

by Valeriy Alexandrovich Astapenko, Frank Bernhard Rosmej and Egor Sergeevich Khramov

Atoms 2020, 8(3), 41; https://doi.org/10.3390/atoms8030041 - 7 Aug 2020

Cited by 4 | Viewed by 2356

Abstract

We investigated theoretically the time dependence of ultra-short laser pulse scattering by an atom at the high-frequency limit for the spectral and total probability of the process using new expression which we derived in this paper. We established that the time dependence of [...] Read more.

We investigated theoretically the time dependence of ultra-short laser pulse scattering by an atom at the high-frequency limit for the spectral and total probability of the process using new expression which we derived in this paper. We established that the time dependence of spectral scattering is presented by the curve with the maximum for sufficiently large detuning of scattering frequency from the carrier frequency of the pulse, while the total scattering probability is always the monotonically increasing function of time. We also studied the dependence of scattering probability on pulse duration at the long-time limit. It was shown that, at the long-pulse limit, the scattering probability is a linear function of pulse duration, while in the opposite case, it is a function with maximum. The position of this maximum is determined by the detuning of the scattering frequency from the carrier frequency of the pulse. Full article

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

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10 pages, 581 KiB

Open AccessArticle

On Laser-Modified Rutherford Scattering

by Sergey A. Zaytsev, Alexander S. Zaytsev, Lorenzo U. Ancarani and Konstantin A. Kouzakov

Atoms 2020, 8(3), 40; https://doi.org/10.3390/atoms8030040 - 3 Aug 2020

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Abstract

We present a theoretical analysis of a charged-particle scattering by a Coulomb potential in the presence of laser radiation. The effect of a laser field is studied using our recently developed nonperturbative parabolic quasi-Sturmian approach for solving the system of coupled Lippmann–Schwinger–Floquet equations [...] Read more.

We present a theoretical analysis of a charged-particle scattering by a Coulomb potential in the presence of laser radiation. The effect of a laser field is studied using our recently developed nonperturbative parabolic quasi-Sturmian approach for solving the system of coupled Lippmann–Schwinger–Floquet equations in the Kramers–Henneberger frame. We calculate the ratio of multiphoton differential cross sections to the Rutherford cross section in the case of a laser-assisted electron-proton scattering process. Our results are compared with predictions of the Bunkin–Fedorov, Kroll–Watson, and Coulomb–Volkov analytical approximations: marked discrepancies are found for different net numbers of exchanged photons and different orientations of the laser-field polarization vector. Our findings clearly demonstrate deficiencies of those well-known approximations for describing laser-modified Rutherford scattering processes. Full article

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

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11 pages, 265 KiB

Open AccessFeature PaperArticle

Configuration–Interaction Perturbation Theory Calculations of Pu II

by Igor Savukov

Atoms 2020, 8(3), 39; https://doi.org/10.3390/atoms8030039 - 30 Jul 2020

Cited by 1 | Viewed by 2201

Abstract

Configuration–interaction perturbation theory (CI–PT) is applied to calculations of low-energy states of Pu II. This ion is quite challenging due to a large number of possible determinants arising from seven valence electrons and strong relativistic effects. The CI–PT calculations agree with experiments for [...] Read more.

Configuration–interaction perturbation theory (CI–PT) is applied to calculations of low-energy states of Pu II. This ion is quite challenging due to a large number of possible determinants arising from seven valence electrons and strong relativistic effects. The CI–PT calculations agree with experiments for the energies and g-factors for many low-energy states that allowed positive identification of the theoretical levels. Isotope shifts were also used to aid in identification, and, in case of the odd states, fitting with three independent parameters was used to match theoretical isotope shifts to the experimental values with good accuracy. The CI–PT approach tested here on the Pu II ion can be generally used to calculate properties of many complex atoms, including U I that can find application in fundamental and applied science. Full article

17 pages, 989 KiB

Open AccessArticle

Radial and Angular Electron Ejection Patterns of Two-Electron Quantum Dots in THz Fields

by Adam Prior, Henri Bachau and Lampros A. A. Nikolopoulos

Atoms 2020, 8(3), 38; https://doi.org/10.3390/atoms8030038 - 21 Jul 2020

Cited by 1 | Viewed by 2634

Abstract

In this work, we develop and apply an ab-initio method to calculate the joint radial- and- angular electron distributions following the interaction of two-electron spherical quantum dots (QD) with intense terahertz pulses of subpicosecond duration. By applying the method to two QDs of [...] Read more.

In this work, we develop and apply an ab-initio method to calculate the joint radial- and- angular electron distributions following the interaction of two-electron spherical quantum dots (QD) with intense terahertz pulses of subpicosecond duration. By applying the method to two QDs of different size, we could investigate two particular ionization mechanisms: the direct and the sequential two-photon double ionization. According to our results, the two ionization mechanisms show some similarity in the angular distribution patterns, whereas the corresponding radial distributions are distinctly different, associated with their joint kinetic energy spectrum. We also discuss the time-evolution of the ionization process in the context of the different nature of the interaction of the QD with the external radiation and the electron–electron correlation interactions. Full article

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

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5 pages, 432 KiB

Open AccessArticle

A Note on the Opacity of the Sun’s Atmosphere

by Anand. K. Bhatia and William. D. Pesnell

Atoms 2020, 8(3), 37; https://doi.org/10.3390/atoms8030037 - 21 Jul 2020

Cited by 2 | Viewed by 3359

Abstract

The opacity of the atmosphere of the Sun is due to processes such as Thomson scattering, bound–bound transitions and photodetachment (bound–free) of hydrogen and positronium ions. The well-studied free–free transitions involving photons, electrons, and hydrogen atoms are re-examined, while free–free transitions involving positrons [...] Read more.

The opacity of the atmosphere of the Sun is due to processes such as Thomson scattering, bound–bound transitions and photodetachment (bound–free) of hydrogen and positronium ions. The well-studied free–free transitions involving photons, electrons, and hydrogen atoms are re-examined, while free–free transitions involving positrons are considered for the first time. Cross sections, averaged over a Maxwellian velocity distribution, involving positrons are comparable to those involving electrons. This indicates that positrons do contribute to the opacity of the atmosphere of the Sun. Accurate results are obtained because definitive phase shifts are known for electron–hydrogen and positron–hydrogen scattering. Full article

(This article belongs to the Special Issue Interactions of Positrons with Matter and Radiation)

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11 pages, 307 KiB

Open AccessArticle

The Spectroscopic Atomic and Molecular Databases at the Paris Observatory

by Evelyne Roueff, Sylvie Sahal-Bréchot, Milan S. Dimitrijević, Nicolas Moreau and Hervé Abgrall

Atoms 2020, 8(3), 36; https://doi.org/10.3390/atoms8030036 - 21 Jul 2020

Cited by 7 | Viewed by 2632

Abstract

This paper is intended to give a comprehensive overview of the current status and developments of the Paris Observatory STARK-B, MOLAT and SESAM databases which can be interrogated thanks to interoperability tools. The STARK-B database provides shifting and broadening parameters of different atomic [...] Read more.

This paper is intended to give a comprehensive overview of the current status and developments of the Paris Observatory STARK-B, MOLAT and SESAM databases which can be interrogated thanks to interoperability tools. The STARK-B database provides shifting and broadening parameters of different atomic and ionic transitions due to impacts with charged particles (the so-called Stark broadening) for different temperatures and densities. The spectroscopic MOLAT and SESAM databases provide the wavelengths, the oscillator strengths or Einstein spontaneous emission coefficients of H

_{2}

, CO and isotopologues molecules. Full article

(This article belongs to the Special Issue Development and Perspectives of Atomic and Molecular Databases)

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14 pages, 479 KiB

Open AccessArticle

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

by Tejaswi Katravulapally and Lampros A. A. Nikolopoulos

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

Cited by 4 | Viewed by 2815

Abstract

The photoionization of Lithium (Li

^{+}

) via its doubly-excited state 2s2p

^{1} P

in intense free electron laser (FEL) radiation is studied. A recently developed perturbative statistical description of the atomic dynamics is used to calculate the ionization yield. It is observed [...] Read more.

The photoionization of Lithium (Li

^{+}

) via its doubly-excited state 2s2p

^{1} P

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

\sim τ_{c} I_{0}

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

^{2 +}

takes over and causes further distortion of the lineshape for Li

^{+}

. Full article

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

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15 pages, 326 KiB

Open AccessArticle

Cobalt-Hydrogen Atomic and Ionic Collisional Data

by Svetlana A. Yakovleva, Andrey K. Belyaev and Maria Bergemann

Atoms 2020, 8(3), 34; https://doi.org/10.3390/atoms8030034 - 13 Jul 2020

Cited by 5 | Viewed by 2252

Abstract

Rate coefficients for inelastic processes in low-energy Co + H,

{Co}^{+} + H^{-}

,

{Co}^{+} + H

, and

{Co}^{2 +} + H^{-}

collisions are estimated using the quantum simplified model. Considerations include 44 triplet and 55 quintet [...] Read more.

Rate coefficients for inelastic processes in low-energy Co + H,

{Co}^{+} + H^{-}

,

{Co}^{+} + H

, and

{Co}^{2 +} + H^{-}

collisions are estimated using the quantum simplified model. Considerations include 44 triplet and 55 quintet molecular states of CoH, as well as 91 molecular states of CoH

^{+}

. The estimations provide the rate coefficients for the 4862 partial processes (mutual neutralization, ion-pair formation, excitation, and de-excitation) in the neutral CoH system, and for the

8190

partial processes in the ionized CoH

^{+}

system,

13, 052

processes in total. At

T = 6000

K, the rate coefficients with the largest values around

6 \times 10^{- 8} {cm}^{3} s^{- 1}

correspond to the mutual neutralization processes into the

Co (e^{2} F) + H

and

{Co}^{+} (g^{5} F) + H

final channels in the neutral and ionized systems, respectively. Among the excitation and de-excitation processes in Co + H and in Co

^{+}

+ H collisions, at

T = 6000

K, the largest rate coefficients have values around

7 \times 10^{- 9} {cm}^{3} s^{- 1}

and correspond to the processes

Co (y^{2} S^{\circ}) + H \to Co (e^{2} F; v^{4} D^{\circ}) + H

and

{Co}^{+} (h^{3} P) + H \to {Co}^{+} (g^{3} P; g^{5} P; g^{5} F) + H

, respectively. The calculations single out inelastic processes important for non-local thermodynamic equilibrium (NLTE) modelling of Co I and Co II spectra in stellar atmospheres. The test NLTE calculations are carried out, and it is found that the new collision rates have a strong effect on the line formation and NLTE abundance corrections. Full article

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

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6 pages, 197 KiB

Open AccessArticle

Two Flavors of Hydrogen Atoms: A Possible Explanation of Dark Matter

by Eugene Oks

Atoms 2020, 8(3), 33; https://doi.org/10.3390/atoms8030033 - 6 Jul 2020

Cited by 14 | Viewed by 3443

Abstract

In one of our previous papers, it was shown that for the ground state of hydrogenic atoms/ions, it is possible to match the interior (inside the nucleus) solution of the Dirac equation with the singular exterior solution of the Dirac equation, so that [...] Read more.

In one of our previous papers, it was shown that for the ground state of hydrogenic atoms/ions, it is possible to match the interior (inside the nucleus) solution of the Dirac equation with the singular exterior solution of the Dirac equation, so that the singular solution should not be rejected for the ground state of hydrogenic atoms/ions. In that paper, there was presented also the first experimental proof of the existence of this Alternative Kind of Hydrogen Atoms (AKHA)—by showing that the presence of the AKHA solves a long-standing mystery of the huge discrepancy between the experimental and previous theoretical results concerning the high-energy tail of the linear momentum distribution in the ground state of hydrogen atoms. In another paper, we showed that for hydrogen atoms, the singular solution of the Dirac equation outside the proton is legitimate not just for the ground state 1²S_1/2, but also for the states 2²S_1/2, 3²S_1/2 and so on: it is legitimate for all the discrete states n²S_1/2. Moreover, the singular exterior solution is legitimate also for the l = 0 states of the continuous spectrum. In that paper, we demonstrated that the AKHA can be the basis for explaining the recent puzzling astrophysical observational results concerning the redshifted radio line 21 cm from the early Universe. Thus, there seems to be the astrophysical evidence of the existence of the AKHA—in addition to the already available observational proof of their existence from atomic experiments. In the present paper, we point out that the AKHA provide an alternative view on dark matter—without resorting to new subatomic particles or dramatically changing the existing physical laws. This is because due to the selection rules, the AKHA do not have state that can be coupled by the electric dipole radiation. We also reformulate the above theoretical results in terms that hydrogen atoms can have two flavors: one flavor corresponding to the regular solution outside the proton, another—to the singular solution outside the proton, both solutions corresponding to the same energy. Since this means the additional degeneracy, then according to the fundamental theorem of quantum mechanics, there should be an additional conserved quantity, which we call isohydrogen spin (isohyspin). Further atomic experiments for accurately measuring the high-energy tail of the linear momentum distribution in the ground state of hydrogen atoms, as well as further observational studies of the redshifted 21 cm radio line from the early Universe, could provide a further proof that dark matter or a part of it is the AKHA. Full article

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