Atoms

8 pages, 1340 KiB

Open AccessArticle

Ionization Cross Sections in the Collision between Two Ground State Hydrogen Atoms at Low Energies

by Saed J. Al Atawneh, Örs Asztalos, Borbála Szondy, Gergő I. Pokol and Károly Tőkési

Atoms 2020, 8(2), 31; https://doi.org/10.3390/atoms8020031 - 22 Jun 2020

Cited by 7 | Viewed by 2973

The interaction between two ground state hydrogen atoms in a collision was studied using the four-body classical trajectory Monte Carlo method. We present the total cross sections for the dominant channels, namely for the single ionization of the target, the ionization of the [...] Read more.

The interaction between two ground state hydrogen atoms in a collision was studied using the four-body classical trajectory Monte Carlo method. We present the total cross sections for the dominant channels, namely for the single ionization of the target, the ionization of the projectile, resulting from pure ionization, and also from the electron transfer (capture or loss) processes. We also present cross sections for the complete break of the system, resulting in the final channel for four free particles. The calculations were carried out at low energies, relevant to the interest of fusion research. We present our cross sections in the projectile energy range between 2.0 keV and 100 keV and compare them with previously obtained theoretical and experimental results. Full article

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

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14 pages, 3558 KiB

Open AccessReview

Atomic Databases: Four of a Kind

by Claudio Mendoza

Atoms 2020, 8(2), 30; https://doi.org/10.3390/atoms8020030 - 19 Jun 2020

Cited by 1 | Viewed by 2932

Abstract

In the context of atomic data computations for astrophysical applications, we review four different types of databases we have implemented for data dissemination: a database for nebular modeling; TIPTOPbase; OPserver; and AtomPy. The database for nebular plasmas is briefly discussed as a study [...] Read more.

In the context of atomic data computations for astrophysical applications, we review four different types of databases we have implemented for data dissemination: a database for nebular modeling; TIPTOPbase; OPserver; and AtomPy. The database for nebular plasmas is briefly discussed as a study case of a successful project. TOPbase and the OPserver were developed during the Opacity Project, an international consortium concerned with the revision of astrophysical opacities, while TIPbase was part of the Iron Project to calculate radiative transition probabilities and electron impact excitation collision strengths for iron-group ions. AtomPy is a prototype for an open, distributed data-assessment environment to engage both producers and users. We discuss design strategies and implementation issues that may help in the undertaking of present and future scientific database projects. Full article

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

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30 pages, 1376 KiB

Open AccessReview

Positron Scattering from Atoms and Molecules

by Sultana N. Nahar and Bobby Antony

Atoms 2020, 8(2), 29; https://doi.org/10.3390/atoms8020029 - 15 Jun 2020

Cited by 8 | Viewed by 4031

Abstract

A review on the positron scattering from atoms and molecules is presented in this article. The focus on positron scattering studies is on the rise due to their presence in various fields and application of cross section data in such environments. Positron scattering [...] Read more.

A review on the positron scattering from atoms and molecules is presented in this article. The focus on positron scattering studies is on the rise due to their presence in various fields and application of cross section data in such environments. Positron scattering is usually investigated using theoretical approaches that are similar to those for electron scattering, being its anti-particle. However, most experimental or theoretical studies are limited to the investigation of electron and positron scattering from inert gases, single electron systems and simple or symmetric molecules. Optical potential and polarized orbital approaches are the widely used methods for investigating positron scattering from atoms. Close coupling approach has also been used for scattering from atoms, but for lighter targets with low energy projectiles. The theoretical approaches have been quite successful in predicting cross sections and agree reasonably well with experimental measurements. The comparison is generally good for electrons for both elastic and inelastic scatterings cross sections, while spin polarization has been critical due to its sensitive perturbing interaction. Positron scattering cross sections show relatively less features than that of electron scattering. The features of positron impact elastic scattering have been consistent with experiment, while total cross section requires significant improvement. For scattering from molecules, utilization of both spherical complex optical potential and R-matrix methods have proved to be efficient in predicting cross sections in their respective energy ranges. The results obtained shows reasonable comparison with most of the existing data, wherever available. In the present article we illustrate these findings with a list of comprehensive references to data sources, albeit not exhaustive. Full article

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

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22 pages, 2845 KiB

Open AccessArticle

High-Temperature Optical Spectra of Diatomic Molecules: Influence of the Avoided Level Crossing

by Robert Beuc and Goran Pichler

Atoms 2020, 8(2), 28; https://doi.org/10.3390/atoms8020028 - 15 Jun 2020

Cited by 5 | Viewed by 2856

Abstract

In this study, we analyzed the light absorption by diatomic molecules or colliding atoms in a spectral region dominated by an avoided crossing of adiabatic state levels or crossing of the corresponding diabatic state levels. Our attention was focused on the low-resolution spectrum [...] Read more.

In this study, we analyzed the light absorption by diatomic molecules or colliding atoms in a spectral region dominated by an avoided crossing of adiabatic state levels or crossing of the corresponding diabatic state levels. Our attention was focused on the low-resolution spectrum at a higher gas temperature under local thermodynamic equilibrium conditions. The absorption measurements of mixed vapors of potassium (≈80%) and cesium (≈20%) were made in the temperature range of 542–715 K and the infrared spectral range 900–1250 nm. In this area, the main spectral contributions were the broad

A^{1} Σ_{(u)}^{+} (0_{(u)}^{+}) - X^{1} Σ_{(g)}^{+} (0_{(g)}^{+})

bands of K₂, Cs_2, and KCs molecules. There was a crossing of

A^{1} Σ_{(u)}^{+} (0_{(u)}^{+})

and

b^{3} Π_{(u)} (0_{(u)}^{+})

state potential curves and the coupling of this state was due to the matrix element

⟨ A^{1} Σ_{(u)}^{+} (0_{(u)}^{+}) | H_{s o} | b^{3} Π_{(u)} (0_{(u)}^{+}) ⟩

of the spin–orbit interaction. Using data for relevant electronic potential curves and transition dipole moments existing in the literature, the spectra of the

A^{1} Σ_{(u)}^{+} (0_{(u)}^{+}) - X^{1} Σ_{(g)}^{+} (0_{(g)}^{+})

molecular bands of K₂, Cs_2, and KCs molecules were calculated. Full quantum mechanical and semi-quantum coupled channel calculations were done and compared with their non-coherent adiabatic or diabatic approximations. Through the comparison of our theoretical and experimental spectra, we identified all observed spectral features and determined the atoms’ number density and gas temperature. Full article

(This article belongs to the Special Issue Atomic and Ionic Collisions with Formation of Quasimolecules)

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Graphical abstract

11 pages, 2397 KiB

Open AccessArticle

Interaction of Be⁴⁺ and Ground State Hydrogen Atom—Classical Treatment of the Collision

by I. Ziaeian and K. Tőkési

Atoms 2020, 8(2), 27; https://doi.org/10.3390/atoms8020027 - 3 Jun 2020

Cited by 16 | Viewed by 3380

Abstract

The interaction between Be⁴⁺ and hydrogen atom is studied using the three-body classical trajectory Monte Carlo method (CTMC) and the quasiclassical trajectory Monte Carlo method of Kirschbaum and Wilets (QTMC-KW). We present total cross sections for target ionization, target excitation, and charge [...] Read more.

The interaction between Be⁴⁺ and hydrogen atom is studied using the three-body classical trajectory Monte Carlo method (CTMC) and the quasiclassical trajectory Monte Carlo method of Kirschbaum and Wilets (QTMC-KW). We present total cross sections for target ionization, target excitation, and charge exchange to the projectile bound states. Calculations are carried out in the projectile energy range between 10 and 1000 keV/au, relevant to the interest of fusion research when the target hydrogen atom is in the ground state. Our results are compared with previous theoretical results. We found that the classical treatment describes reasonably well the cross sections for various final channels. Moreover, we show that the calculations by the QTMC-KW model significantly improve the obtained cross sections. Full article

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

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12 pages, 5838 KiB

Open AccessEditor’s ChoiceArticle

Deep Minima in the Triply Differential Cross Section for Ionization of Atomic Hydrogen by Electron and Positron Impact

by C. M. DeMars, S. J. Ward, J. Colgan, S. Amami and D. H. Madison

Atoms 2020, 8(2), 26; https://doi.org/10.3390/atoms8020026 - 29 May 2020

Cited by 9 | Viewed by 2966

Abstract

We investigate ionization of atomic hydrogen by electron- and positron-impact. We apply the Coulomb–Born (CB1) approximation, various modified CB1 approximations, the three body distorted wave (3DW) approximation, and the time-dependent close-coupling (TDCC) method to electron-impact ionization of hydrogen. For electron-impact ionization of hydrogen [...] Read more.

We investigate ionization of atomic hydrogen by electron- and positron-impact. We apply the Coulomb–Born (CB1) approximation, various modified CB1 approximations, the three body distorted wave (3DW) approximation, and the time-dependent close-coupling (TDCC) method to electron-impact ionization of hydrogen. For electron-impact ionization of hydrogen for an incident energy of approximately 76.45 eV, we obtain a deep minimum in the CB1 triply differential cross section (TDCS). However, the TDCC for 74.45 eV and the 3DW for 74.46 eV gave a dip in the TDCS. For positron-hydrogen ionization (breakup) we apply the CB1 approximation and a modified CB1 approximation. We obtain a deep minimum in the TDCS and a zero in the CB1 transition matrix element for an incident energy of 100 eV with a gun angle of

{56.13}^{°}

. Corresponding to a zero in the CB1 transition matrix element, there is a vortex in the velocity field associated with this element. For both electron- and positron-impact ionization of hydrogen the velocity field rotates in the same direction, which is anticlockwise. All calculations are performed for a doubly symmetric geometry; the electron-impact ionization is in-plane and the positron-impact ionization is out-of-plane. Full article

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

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30 pages, 14111 KiB

Open AccessReview

Laboratory Courses on Laser Spectroscopy and Atom Trapping

by Hermina C. Beica, Shoshana Winter, Carson Mok, Brynle Barrett, Rob Berthiaume, Andrejs Vorozcovs, Fadi Yachoua, Nima Afkhami-Jeddi, Monika Aggarwal, Gehrig Carlse, Alex Pouliot, Kevin B. Borsos, Thomas Vacheresse, Raanan Marants and A. Kumarakrishnan

Atoms 2020, 8(2), 25; https://doi.org/10.3390/atoms8020025 - 28 May 2020

Cited by 1 | Viewed by 3588

Abstract

We present an overview of experiments covered in two semester-length laboratory courses dedicated to laser spectroscopy and atom trapping. These courses constitute a powerful approach for teaching experimental physics in a manner that is both contemporary and capable of providing the background and [...] Read more.

We present an overview of experiments covered in two semester-length laboratory courses dedicated to laser spectroscopy and atom trapping. These courses constitute a powerful approach for teaching experimental physics in a manner that is both contemporary and capable of providing the background and skills relevant to a variety of research laboratories. The courses are designed to be accessible for all undergraduate streams in physics and applied physics as well as incoming graduate students. In the introductory course, students carry out several experiments in atomic and laser physics. In a follow up course, students trap atoms in a magneto-optical trap and carry out preliminary investigations of the properties of laser cooled atoms based on the expertise acquired in the first course. We discuss details of experiments, impact, possible course formats, budgetary requirements, and challenges related to long-term maintenance. Full article

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9 pages, 1330 KiB

Open AccessArticle

Photoionization of KCs Molecule: Origin of the Structured Continuum?

by Goran Pichler, Robert Beuc, Jahja Kokaj, David Sarkisyan, Nimmy Jose and Joseph Mathew

Atoms 2020, 8(2), 24; https://doi.org/10.3390/atoms8020024 - 28 May 2020

Cited by 5 | Viewed by 3090

Abstract

We report the experimental observation of photoionization bands of the KCs molecule in the deep ultraviolet spectral region between 200 and 420 nm. We discuss the origin of observed photoionization bands as stemming from the absorption from the ground state of the KCs [...] Read more.

We report the experimental observation of photoionization bands of the KCs molecule in the deep ultraviolet spectral region between 200 and 420 nm. We discuss the origin of observed photoionization bands as stemming from the absorption from the ground state of the KCs molecule to the excited states of KCs⁺ molecule for which we used existing potential curves of the KCs⁺ molecule. An alternative explanation relies on the absorption from the ground state of the KCs molecule to the doubly excited states of the KCs^** molecule, situated above the lowest molecular state of KCs⁺. The relevant potential curves of KCs^** are not known yet, but all those KCs** potential curves are certainly autoionizing. However, these two photoionization pathways may interfere resulting in a special interference structured continuum, which is observed as complex bands. Full article

(This article belongs to the Special Issue Atomic and Ionic Collisions with Formation of Quasimolecules)

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Graphical abstract

14 pages, 2158 KiB

Open AccessEditor’s ChoiceArticle

The Optogalvanic Spectrum of Neutral Lanthanum between 5610 and 6110 Å

by Laurentius Windholz and Tobias Binder

Atoms 2020, 8(2), 23; https://doi.org/10.3390/atoms8020023 - 19 May 2020

Cited by 8 | Viewed by 2669

Abstract

We report on a complete optogalvanic spectrum of a discharge burning in a La-Ar gas mixture, in the spectral range 5610–6110 Å (17,851 to 16,364 cm⁻¹). About 1900 overlapping laser scans, each between 1 and 1.5 cm⁻¹ wide, were necessary [...] Read more.

We report on a complete optogalvanic spectrum of a discharge burning in a La-Ar gas mixture, in the spectral range 5610–6110 Å (17,851 to 16,364 cm⁻¹). About 1900 overlapping laser scans, each between 1 and 1.5 cm⁻¹ wide, were necessary to cover this range. The resolution of the spectra is limited by the Doppler width of the spectral features to about 0.03 cm⁻¹ (or ca. 0.01 Å) and is comparable with a Fourier-transform spectrum, but the sensitivity is much higher. Indeed, we could find more than 1800 lines, from which about 800 could be classified as transitions between known energy levels. The main focus of the investigations was to discover previously unknown energy levels by means of excitation of unclassified spectral features. Full article

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

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15 pages, 377 KiB

Open AccessArticle

Branching Ratio and CP Violation in B s 0 ¯ → ϕϕ Decay in the Framework of QCD Factorization

by E. H. Raslan and H. R. Khan

Atoms 2020, 8(2), 22; https://doi.org/10.3390/atoms8020022 - 16 May 2020

Cited by 2 | Viewed by 2703

Abstract

We present an analytic calculation of Branching Ratio (BR) and Charge-Parity (CP) violating asymmetries of the

\bar{B_{s}^{0}}

meson decay into the two light vectors

ϕ ϕ

. In doing this we calculate the helicity amplitude of [...] Read more.

We present an analytic calculation of Branching Ratio (BR) and Charge-Parity (CP) violating asymmetries of the

\bar{B_{s}^{0}}

meson decay into the two light vectors

ϕ ϕ

. In doing this we calculate the helicity amplitude of the present decay in the framework of QCD factorization approach. We find the BR of

\bar{B_{s}^{0}} \to ϕ ϕ = (1.56 \pm 0.23) \times 10^{- 5}

. We also calculate the direct CP violation, CP violation in mixing and CP violation due to interference which are

A_{C P}^{dir} = 0.00355 \pm 0.00152

,

A_{C P}^{mix} = - 0.00629 \pm 0.03119

and

A_{C P}^{Δ Γ} = 0.99997 \pm 0.00019

, respectively. Our results are in agreement with the recent theoretical predictions and experimental measurements. Full article

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18 pages, 694 KiB

Open AccessEditor’s ChoiceReview

A Laboratory Astrophysics Problem: The Lifetime of Very Long-Lived Levels in Low-Charge Ions

by Elmar Träbert

Atoms 2020, 8(2), 21; https://doi.org/10.3390/atoms8020021 - 11 May 2020

Cited by 8 | Viewed by 2878

Abstract

Emission lines of singly charged ions populate many astrophysical spectra. However, the interpretation of the line intensities (usually line ratios) often depends on the transition rates of the decays of very long-lived low-lying levels. For example, the line ratio of two electric-dipole forbidden [...] Read more.

Emission lines of singly charged ions populate many astrophysical spectra. However, the interpretation of the line intensities (usually line ratios) often depends on the transition rates of the decays of very long-lived low-lying levels. For example, the line ratio of two electric-dipole forbidden transitions in the 3s

^{2}

3p

^{3}

ground configuration of singly ionized sulfur (ion S

^{+}

, spectrum S II) has been interpreted in terms of a density diagnostic for planetary nebulae, i.e., for densities in the order of 10

^{4}

cm

^{- 3}

. The predicted lifetimes of the

^{2}

D

_{3 / 2, 5 / 2}^{o}

levels are in the order of one hour. Modeling indicates that a 10% uncertainty of the lifetime determination in this case corresponds to a 50% uncertainty of the density diagnostic. The available theoretical lifetime predictions scatter by much more than 10%. Considerations about an experimental approach are presented with the goal of instigating a measurement of the actual level lifetimes. Full article

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

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7 pages, 204 KiB

Open AccessArticle

Resonances in Systems Involving Positrons

by Anand K. Bhatia

Atoms 2020, 8(2), 20; https://doi.org/10.3390/atoms8020020 - 7 May 2020

Cited by 2 | Viewed by 2272

Abstract

When an incident particle on a target gets attached to the target, the cross-section at that energy could be much larger compared to those at other energies. This is a short-lived state and decays by emitting an electron. Such states can also be [...] Read more.

When an incident particle on a target gets attached to the target, the cross-section at that energy could be much larger compared to those at other energies. This is a short-lived state and decays by emitting an electron. Such states can also be formed by the absorption of a photon. Such states are below the higher thresholds and are called autoionization states, doubly excited states, or Feshbach resonances. There is also a possibility of such states to form above the thresholds. Then they are called shape resonances. Resonances are important in the diagnostic of solar and astrophysical plasmas. Some methods of calculating the resonance parameters are described and resonance parameters occurring in various systems are given. Full article

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

9 pages, 2464 KiB

Open AccessArticle

Doubly and Triply Differential Cross Sections for Single Ionization of He by Fast Au⁵³⁺ Using a Multi-Body Quasiclassical Model

by François Frémont

Atoms 2020, 8(2), 19; https://doi.org/10.3390/atoms8020019 - 6 May 2020

Cited by 1 | Viewed by 2221

Abstract

A multi-body multi-center quasiclassical model was used to determine doubly- and triply-differential cross sections following single ionization in 3.6 MeV/amu Au⁵³⁺ + He collisions. The present model improved recent calculations, in which free electrons were added in the collision to reproduce, at [...] Read more.

A multi-body multi-center quasiclassical model was used to determine doubly- and triply-differential cross sections following single ionization in 3.6 MeV/amu Au⁵³⁺ + He collisions. The present model improved recent calculations, in which free electrons were added in the collision to reproduce, at least qualitatively, the experimental binary peak. In the present calculations, the electrons, that were assumed to originate from the collisions of Au⁵³⁺ with surfaces before colliding with the He target, were now considered to be in the field of the projectile, with nearly the same velocity. The agreement between the calculations and the experiment was improved, for both the doubly- and the triply-differential cross sections and was better than previous calculations based on quantum mechanics. Full article

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

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20 pages, 2354 KiB

Open AccessEditor’s ChoiceArticle

Current Status and Developments of the Atomic Database on Rare-Earths at Mons University (DREAM)

by Pascal Quinet and Patrick Palmeri

Atoms 2020, 8(2), 18; https://doi.org/10.3390/atoms8020018 - 2 May 2020

Cited by 16 | Viewed by 3044

Abstract

The main purpose of the Database on Rare Earths At Mons University (DREAM) is to provide the scientific community with updated spectroscopic parameters related to lanthanide atoms (Z = 57–71) in their lowest ionization stages. The radiative parameters (oscillator strengths and transitions [...] Read more.

The main purpose of the Database on Rare Earths At Mons University (DREAM) is to provide the scientific community with updated spectroscopic parameters related to lanthanide atoms (Z = 57–71) in their lowest ionization stages. The radiative parameters (oscillator strengths and transitions probabilities) listed in the database have been obtained over the past 20 years by the Atomic Physics and Astrophysics group of Mons University, Belgium, thanks to a systematic and extensive use of the pseudo-relativistic Hartree-Fock (HFR) method modified for taking core-polarization and core-penetration effects into account. Most of these theoretical results have been validated by the good agreement obtained when comparing computed radiative lifetimes and accurate experimental values measured by the time-resolved laser-induced fluorescence technique. In the present paper, we report on the current status and developments of the database that gathers radiative parameters for more than 72,000 spectral lines in neutral, singly-, doubly-, and triply-ionized lanthanides. Full article

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

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12 pages, 1756 KiB

Open AccessArticle

Low-Energy Electron Elastic Total Cross Sections for Ho, Er, Tm, Yb, Lu, and Hf Atoms

by Zineb Felfli and Alfred Z. Msezane

Atoms 2020, 8(2), 17; https://doi.org/10.3390/atoms8020017 - 30 Apr 2020

Cited by 4 | Viewed by 2712

Abstract

The robust Regge-pole methodology wherein is fully embedded the essential electron-electron correlation effects and the vital core polarization interaction has been used to explore negative ion formation in the large lanthanide Ho, Er, Tm, Yb, Lu, and Hf atoms through the electron elastic [...] Read more.

The robust Regge-pole methodology wherein is fully embedded the essential electron-electron correlation effects and the vital core polarization interaction has been used to explore negative ion formation in the large lanthanide Ho, Er, Tm, Yb, Lu, and Hf atoms through the electron elastic total cross sections (TCSs) calculations. These TCSs are characterized generally by dramatically sharp resonances manifesting ground, metastable, and excited negative ion formation during the collisions, Ramsauer-Townsend minima, and shape resonances. The novelty and generality of the Regge-pole approach is in the extraction of the negative ion binding energies (BEs) of complex heavy systems from the calculated electron TCSs. The extracted anionic BEs from the ground state TCSs for Ho, Er, Tm, Yb, Lu, and Hf atoms are 3.51 eV, 3.53 eV, 3.36 eV, 3.49 eV, 4.09 eV and 1.68 eV, respectively. The TCSs are presented and the extracted from the ground; metastable and excited anionic states BEs are compared with the available measured and/or calculated electron affinities. We conclude with a remark on the existing inconsistencies in the meaning of the electron affinity among the various measurements and/or calculations in the investigated atoms and make a recommendation to resolve the ambiguity. Full article

(This article belongs to the Special Issue Atomic Structure and Scattering: Comparative Theoretical Calculations and Uncertainties)

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12 pages, 518 KiB

Open AccessEditor’s ChoiceArticle

Referencing Sources of Molecular Spectroscopic Data in the Era of Data Science: Application to the HITRAN and AMBDAS Databases

by Frances M. Skinner, Iouli E. Gordon, Christian Hill, Robert J. Hargreaves, Kelly E. Lockhart and Laurence S. Rothman

Atoms 2020, 8(2), 16; https://doi.org/10.3390/atoms8020016 - 30 Apr 2020

Cited by 6 | Viewed by 4401

Abstract

The application described has been designed to create bibliographic entries in large databases with diverse sources automatically, which reduces both the frequency of mistakes and the workload for the administrators. This new system uniquely identifies each reference from its digital object identifier (DOI) [...] Read more.

The application described has been designed to create bibliographic entries in large databases with diverse sources automatically, which reduces both the frequency of mistakes and the workload for the administrators. This new system uniquely identifies each reference from its digital object identifier (DOI) and retrieves the corresponding bibliographic information from any of several online services, including the SAO/NASA Astrophysics Data Systems (ADS) and CrossRef APIs. Once parsed into a relational database, the software is able to produce bibliographies in any of several formats, including HTML and BibTeX, for use on websites or printed articles. The application is provided free-of-charge for general use by any scientific database. The power of this application is demonstrated when used to populate reference data for the HITRAN and AMBDAS databases as test cases. HITRAN contains data that is provided by researchers and collaborators throughout the spectroscopic community. These contributors are accredited for their contributions through the bibliography produced alongside the data returned by an online search in HITRAN. Prior to the work presented here, HITRAN and AMBDAS created these bibliographies manually, which is a tedious, time-consuming and error-prone process. The complete code for the new referencing system can be found on the HITRANonline GitHub website. Full article

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

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24 pages, 333 KiB

Open AccessFeature PaperEditor’s ChoiceReview

The Leiden Atomic and Molecular Database (LAMDA): Current Status, Recent Updates, and Future Plans

by Floris F. S. van der Tak, François Lique, Alexandre Faure, John H. Black and Ewine F. van Dishoeck

Atoms 2020, 8(2), 15; https://doi.org/10.3390/atoms8020015 - 28 Apr 2020

Cited by 75 | Viewed by 4637

Abstract

The Leiden Atomic and Molecular Database (LAMDA) collects spectroscopic information and collisional rate coefficients for molecules, atoms, and ions of astrophysical and astrochemical interest. We describe the developments of the database since its inception in 2005, and outline our plans for the near [...] Read more.

The Leiden Atomic and Molecular Database (LAMDA) collects spectroscopic information and collisional rate coefficients for molecules, atoms, and ions of astrophysical and astrochemical interest. We describe the developments of the database since its inception in 2005, and outline our plans for the near future. Such a database is constrained both by the nature of its uses and by the availability of accurate data: we suggest ways to improve the synergies among users and suppliers of data. We summarize some recent developments in computation of collisional cross sections and rate coefficients. We consider atomic and molecular data that are needed to support astrophysics and astrochemistry with upcoming instruments that operate in the mid- and far-infrared parts of the spectrum. Full article

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

12 pages, 2551 KiB

Open AccessReview

Positron Processes in the Sun

by Nat Gopalswamy

Atoms 2020, 8(2), 14; https://doi.org/10.3390/atoms8020014 - 22 Apr 2020

Cited by 5 | Viewed by 4630

Abstract

Positrons play a major role in the emission of solar gamma-rays at energies from a few hundred keV to >1 GeV. Although the processes leading to positron production in the solar atmosphere are well known, the origin of the underlying energetic particles that [...] Read more.

Positrons play a major role in the emission of solar gamma-rays at energies from a few hundred keV to >1 GeV. Although the processes leading to positron production in the solar atmosphere are well known, the origin of the underlying energetic particles that interact with the ambient particles is poorly understood. With the aim of understanding the full gamma-ray spectrum of the Sun, I review the key emission mechanisms that contribute to the observed gamma-ray spectrum, focusing on the ones involving positrons. In particular, I review the processes involved in the 0.511 MeV positron annihilation line and the positronium continuum emissions at low energies, and the pion continuum emission at high energies in solar eruptions. It is thought that particles accelerated at the flare reconnection and at the shock driven by coronal mass ejections are responsible for the observed gamma-ray features. Based on some recent developments I suggest that energetic particles from both mechanisms may contribute to the observed gamma-ray spectrum in the impulsive phase, while the shock mechanism is responsible for the extended phase. Full article

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

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13 pages, 549 KiB

Open AccessArticle

Analytical Results for the Three-Body Radiative Attachment Rate Coefficient, with Application to the Positive Antihydrogen Ion H⁺

by Jack C. Straton

Atoms 2020, 8(2), 13; https://doi.org/10.3390/atoms8020013 - 20 Apr 2020

Cited by 1 | Viewed by 2270

Abstract

To overcome the numerical difficulties inherent in the Maxwell–Boltzmann integral of the velocity-weighted cross section that gives the radiative attachment rate coefficient

α_{R A}

for producing the negative hydrogen ion H

^{-}

or its antimatter equivalent, the positive antihydrogen ion [...] Read more.

To overcome the numerical difficulties inherent in the Maxwell–Boltzmann integral of the velocity-weighted cross section that gives the radiative attachment rate coefficient

α_{R A}

for producing the negative hydrogen ion H

^{-}

or its antimatter equivalent, the positive antihydrogen ion

{\bar{H}}^{+}

, we found the analytic form for this integral. This procedure is useful for temperatures below 700 K, the region for which the production of

{\bar{H}}^{+}

has potential use as an intermediate stage in the cooling of antihydrogen to ultra-cold (sub-mK) temperatures for spectroscopic studies and probing the gravitational interaction of the anti-atom. Our results, utilizing a 50-term explicitly correlated exponential wave function, confirm our prior numerical results. Full article

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

13 pages, 1007 KiB

Open AccessEditor’s ChoiceArticle

Elastic Photon Scattering on Hydrogenic Atoms near Resonances

by Dmitrii Samoilenko, Andrey V. Volotka and Stephan Fritzsche

Atoms 2020, 8(2), 12; https://doi.org/10.3390/atoms8020012 - 18 Apr 2020

Cited by 6 | Viewed by 2703

Abstract

Scattering of light on relativistic heavy ion beams is widely used for characterizing and tuning the properties of both the light and the ion beam. Its elastic component—Rayleigh scattering—is investigated in this work for photon energies close to certain electronic transitions because of [...] Read more.

Scattering of light on relativistic heavy ion beams is widely used for characterizing and tuning the properties of both the light and the ion beam. Its elastic component—Rayleigh scattering—is investigated in this work for photon energies close to certain electronic transitions because of its potential usage in the Gamma Factory initiative at CERN. The angle-differential cross-section, as well as the degree of polarization of the scattered light are investigated for the cases of

1 s - 2 p_{1 / 2}

and

1 s - 2 p_{3 / 2}

resonance transitions in H-like lead ions. In order to gauge the validity and uncertainty of frequently used approximations, we compare different methods. In particular, rigorous quantum electrodynamics calculations are compared with the resonant electric-dipole approximation evaluated within the relativistic and nonrelativistic formalisms. For better understanding of the origin of the approximation, the commonly used theoretical approach is explained here in detail. We find that in most cases, the nonrelativistic resonant electric-dipole approximation fails to describe the properties of the scattered light. At the same time, its relativistic variant agrees with the rigorous treatment within a level of 10% to 20%. These findings are essential for the design of an experimental setup exploiting the scattering process, as well as for the determination of the scattered light properties. Full article

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4 pages, 178 KiB

Open AccessReview

A Precis of Threshold Laws for Positron vs. Electron Impact Ionization of Atoms

by A. Temkin

Atoms 2020, 8(2), 11; https://doi.org/10.3390/atoms8020011 - 10 Apr 2020

Viewed by 2100

Abstract

The Coulomb-dipole theory of positron vs. electron impact ionization of hydrogen (as a proxy for neutral atoms) is reviewed, emphasizing how the analytic form of the threshold law (but not the magnitude) can be the same, whereas the physics of each is entirely [...] Read more.

The Coulomb-dipole theory of positron vs. electron impact ionization of hydrogen (as a proxy for neutral atoms) is reviewed, emphasizing how the analytic form of the threshold law (but not the magnitude) can be the same, whereas the physics of each is entirely different. Full article

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

9 pages, 1036 KiB

Open AccessEditor’s ChoiceArticle

Differential Study of Projectile Coherence Effects on Double Capture Processes in p + Ar Collisions

by Trevor Voss, Basu R. Lamichhane, Madhav Dhital, Ramaz Lomsadze and Michael Schulz

Atoms 2020, 8(2), 10; https://doi.org/10.3390/atoms8020010 - 28 Mar 2020

Cited by 2 | Viewed by 3171

Abstract

We have measured differential yields for double capture and double capture accompanied by ionization in 75 keV p + Ar collisions. Data were taken for two different transverse projectile coherence lengths. A small effect of the projectile coherence properties on the yields were [...] Read more.

We have measured differential yields for double capture and double capture accompanied by ionization in 75 keV p + Ar collisions. Data were taken for two different transverse projectile coherence lengths. A small effect of the projectile coherence properties on the yields were found for double capture, but not for double capture plus ionization. The results suggest that multiple projectile–target interactions can lead to a significant weakening of projectile coherence effects. Full article

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

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Atoms, Volume 8, Issue 2 (June 2020) – 22 articles

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