Editorial

2 pages, 156 KiB

Open AccessEditorial

Special Issue on Atomic and Ionic Collisions with Formation of Quasimolecules

by Vladimir A. Srećković, Milan S. Dimitrijević and Nikolai N. Bezuglov

Atoms 2019, 7(1), 3; https://doi.org/10.3390/atoms7010003 - 28 Dec 2018

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Many areas of science today, like atomic and molecular physics, nuclear physics, astrophysics, laboratory plasma research etc., depend on data for ionic, atomic, and molecular collision processes. The purpose of the Special Issue “Atomic and Ionic Collisions with Formation of Quasimolecules” in Atoms [...] Read more.

Many areas of science today, like atomic and molecular physics, nuclear physics, astrophysics, laboratory plasma research etc., depend on data for ionic, atomic, and molecular collision processes. The purpose of the Special Issue “Atomic and Ionic Collisions with Formation of Quasimolecules” in Atoms is to engage a broad community of researchers to consolidate knowledge, make new discoveries, and to continue the exchange of ideas. Full article

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

Research

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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 2473

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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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 2754

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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28 pages, 735 KiB

Open AccessArticle

Electron Broadening Operator Including Penetrating Collisions for Hydrogen

by Jean-Christophe Pain and Franck Gilleron

Atoms 2020, 8(1), 2; https://doi.org/10.3390/atoms8010002 - 14 Jan 2020

Cited by 1 | Viewed by 2176

Abstract

The expression of the electron broadening operator including the effect of penetrating collisions, i.e., for which the incoming electron enters the extent of bound-electron wave-functions, is rather complicated, even for hydrogen. It involves integrals of special functions, the evaluation of which deserves scrutiny. [...] Read more.

The expression of the electron broadening operator including the effect of penetrating collisions, i.e., for which the incoming electron enters the extent of bound-electron wave-functions, is rather complicated, even for hydrogen. It involves integrals of special functions, the evaluation of which deserves scrutiny. We present a simple approximate form of the electron collision operator for hydrogen including penetration effects, both in direct and interference terms. The new expression is accurate and easy to compute. In the Penetration Standard Theory, the collision operator is convergent whatever the value of the maximum impact parameter. However, when penetration theory is not valid anymore, it should be questioned. We discuss the problem of strong collisions when penetration effects are taken into account. Full article

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

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9 pages, 1199 KiB

Open AccessArticle

Stark Widths Regularities Within: ns-np, np-ns, np-nd, nd-np and nd-nf Spectral Series of Potassium Isoelectronic Sequence

by Nora Trklja, Ivan P. Dojčinović, Irinel Tapalaga and Jagoš Purić

Atoms 2019, 7(4), 99; https://doi.org/10.3390/atoms7040099 - 31 Oct 2019

Cited by 2 | Viewed by 2167

Abstract

Results presented in this paper show a regular behaviour of Stark widths within the studied spectral series of potassium isoelectronic sequence. These regularities have been found and verified on the basis of the existing theoretical and experimental data being normalized for the same [...] Read more.

Results presented in this paper show a regular behaviour of Stark widths within the studied spectral series of potassium isoelectronic sequence. These regularities have been found and verified on the basis of the existing theoretical and experimental data being normalized for the same plasma conditions (chosen electron density and temperature). Using the available set of data the corresponding formulas expressing the Stark widths of the lines originated from the spectral series studied here as a function of the upper-level ionization potential and the rest core charge of the emitter seeing by the electron undergoing transition, are obtained here. Well established and verified dependence is used to calculate Stark width data needed but not available so far. For the purposes of the operation with a large number of data, algorithms for the analysis of Stark width dependence on temperature and electron density and for the investigation of the assumed correlation between Stark width and ionization potential of the upper level of analyzed transition, have been made. Developed algorithms enable fast data processing. Full article

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

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14 pages, 28438 KiB

Open AccessArticle

Channeling of Protons through Radial Deformed Double Wall Carbon Nanotubes

by Duško Borka and Vesna Borka Jovanović

Atoms 2019, 7(3), 88; https://doi.org/10.3390/atoms7030088 - 07 Sep 2019

Cited by 2 | Viewed by 2553

Abstract

In this study we presented a theoretical investigation of the channeling of high energy protons with the radial deformed (10, 0)@(5, 0) double-wall carbon nanotubes (DWNTs). Proton energy is varied from 0.1 to 10 GeV. The channeling potential within the deformed DWNTs is [...] Read more.

In this study we presented a theoretical investigation of the channeling of high energy protons with the radial deformed (10, 0)@(5, 0) double-wall carbon nanotubes (DWNTs). Proton energy is varied from 0.1 to 10 GeV. The channeling potential within the deformed DWNTs is presented. A Monte Carlo (MC) simulation is used to obtain spatial and angular distributions of channeled protons with radially deformed DWNTs. We treated problem relativistically. This is the first time that we presented spatial and angular distributions of channeled protons with radially deformed DWNTs. Our results show that the spatial and angular distributions depend strongly of nanotube lengths, proton energy, and especially of level of radial deformation of nanotube. Multi-wall nanotubes (MWNTs) can be technically realised with better channeling performance then single-wall nanotubes (SWNTs) and that is why we believe that these results may be useful for production and guiding of nanosized ion beams. Full article

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

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8 pages, 747 KiB

Open AccessArticle

Stark Broadening of Neutral Boron Lines

by Magdalena Christova, Milan S. Dimitrijević and Sylvie Sahal-Bréchot

Atoms 2019, 7(3), 80; https://doi.org/10.3390/atoms7030080 - 19 Aug 2019

Cited by 1 | Viewed by 2294

Abstract

Stark broadening parameters, width and shift, of lines within B I 2s²2p–2s²ns spectral series have been calculated. Semi-classical theory in impact approximation has been applied. Temperature dependence of Stark parameters has been studied. The presented results could be applied for plasma diagnostics. Full article

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

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13 pages, 2724 KiB

Open AccessArticle

On the Approximate Evaluation of Some Oscillatory Integrals

by Robert Beuc, Mladen Movre and Berislav Horvatić

Atoms 2019, 7(2), 47; https://doi.org/10.3390/atoms7020047 - 05 May 2019

Cited by 2 | Viewed by 2692

Abstract

To determine the photon emission or absorption probability for a diatomic system in the context of the semiclassical approximation it is necessary to calculate the characteristic canonical oscillatory integral which has one or more saddle points. Integrals like that appear in a whole [...] Read more.

To determine the photon emission or absorption probability for a diatomic system in the context of the semiclassical approximation it is necessary to calculate the characteristic canonical oscillatory integral which has one or more saddle points. Integrals like that appear in a whole range of physical problems, e.g., the atom–atom and atom–surface scattering and various optical phenomena. A uniform approximation of the integral, based on the stationary phase method is proposed, where the integral with several saddle points is replaced by a sum of integrals each having only one or at most two real saddle points and is easily soluble. In this way we formally reduce the codimension in canonical integrals of “elementary catastrophes” with codimensions greater than 1. The validity of the proposed method was tested on examples of integrals with three saddle points (“cusp” catastrophe) and four saddle points (“swallow-tail” catastrophe). Full article

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

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6 pages, 239 KiB

Open AccessArticle

Stark Widths of Yb III and Lu IV Spectral Lines

by Milan S. Dimitrijević

Atoms 2019, 7(1), 10; https://doi.org/10.3390/atoms7010010 - 10 Jan 2019

Cited by 2 | Viewed by 2378

Abstract

Rare Earth Elements are important for stellar atmosphere analysis but the corresponding Stark broadening data are scarce. For Yb III and Lu IV theoretical as well as experimental data on Stark broadening parameters of spectral lines are absent in the literature. Using the [...] Read more.

Rare Earth Elements are important for stellar atmosphere analysis but the corresponding Stark broadening data are scarce. For Yb III and Lu IV theoretical as well as experimental data on Stark broadening parameters of spectral lines are absent in the literature. Using the modified semiempirical method of Dimitrijević and Konjević, we determined Stark widths for four Yb III and four Lu IV transitions, belonging to the erbium isoelectronic sequence. The obtained results are also used to discuss similarities between homologous transitions in the erbium isoelectronic sequence. We note as well that calculated widths will be implemented in the STARK-B database which is also a part of the Virtual Atomic and Molecular Data Center. Full article

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

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