Atoms

4 pages, 357 KiB

Open AccessFeature PaperArticle

Influence of Helical Trajectories of Perturbers on Stark Line Shapes in Magnetized Plasmas

by J. Rosato, S. Ferri and R. Stamm

Atoms 2018, 6(1), 12; https://doi.org/10.3390/atoms6010012 - 13 Mar 2018

Cited by 12 | Viewed by 2829

In plasmas subject to a strong magnetic field, the dynamical properties of the microfield are affected by the cyclotron motion, which can alter Stark-broadened lines. We illustrate this effect through calculations of the hydrogen Lyman

α

line in an ideal one-component plasma. A [...] Read more.

In plasmas subject to a strong magnetic field, the dynamical properties of the microfield are affected by the cyclotron motion, which can alter Stark-broadened lines. We illustrate this effect through calculations of the hydrogen Lyman

α

line in an ideal one-component plasma. A focus is put on the central Zeeman component. It is shown that the atomic dipole autocorrelation function decreases more slowly if the cyclotron motion is retained. In the frequency domain, this denotes a reduction of the line broadening. A discussion based on numerical simulations and analytical estimates is done. Full article

(This article belongs to the Special Issue Spectral Line Shapes in Plasmas II)

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20 pages, 882 KiB

Open AccessFeature PaperArticle

ZEST: A Fast Code for Simulating Zeeman-Stark Line-Shape Functions

by Franck Gilleron and Jean-Christophe Pain

Atoms 2018, 6(1), 11; https://doi.org/10.3390/atoms6010011 - 12 Mar 2018

Cited by 5 | Viewed by 4007

Abstract

We present the ZEST code, dedicated to the calculation of line shapes broadened by Zeeman and Stark effects. As concerns the Stark effect, the model is based on the Standard Lineshape Theory in which ions are treated in the quasi-static approximation, whereas the [...] Read more.

We present the ZEST code, dedicated to the calculation of line shapes broadened by Zeeman and Stark effects. As concerns the Stark effect, the model is based on the Standard Lineshape Theory in which ions are treated in the quasi-static approximation, whereas the effects of electrons are represented by weak collisions in the framework of a binary collision relaxation theory. A static magnetic field may be taken into account in the radiator Hamiltonian in the dipole approximation, which leads to additional Zeeman splitting patterns. Ion dynamics effects are implemented using the fast Frequency-Fluctuation Model. For fast calculations, the static ion microfield distribution in the plasma is evaluated using analytic fits of Monte-Carlo simulations, which depend only on the ion-ion coupling parameter and the electron-ion screening factor. Full article

(This article belongs to the Special Issue Spectral Line Shapes in Plasmas II)

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7 pages, 750 KiB

Open AccessFeature PaperArticle

Stark Broadening of Se IV, Sn IV, Sb IV and Te IV Spectral Lines

by Milan S. Dimitrijević, Zoran Simić, Roland Stamm, Joël Rosato, Nenad Milovanović and Cristina Yubero

Atoms 2018, 6(1), 10; https://doi.org/10.3390/atoms6010010 - 07 Mar 2018

Cited by 8 | Viewed by 3013

Abstract

Stark broadening parameters, line width and shift, are needed for investigations, analysis and modelling of astrophysical, laboratory, laser produced and technological plasmas. Especially in astrophysics, due to constantly increasing resolution of satellite borne spectrographs, and large terrestrial telescopes, data on trace elements, which [...] Read more.

Stark broadening parameters, line width and shift, are needed for investigations, analysis and modelling of astrophysical, laboratory, laser produced and technological plasmas. Especially in astrophysics, due to constantly increasing resolution of satellite borne spectrographs, and large terrestrial telescopes, data on trace elements, which were previously insignificant, now have increasing importance. Using the modified semiempirical method of Dimitrijević and Konjević, here, Stark widths have been calculated for 2 Se IV, 6 Sn IV, 2 Sb IV and 1 Te IV transitions. Results have been compared with existing theoretical data for Sn IV. Obtained results will be implemented in the STARK-B database, which is also a part of Virtual atomic and molecular data center (VAMDC). Full article

(This article belongs to the Special Issue Spectral Line Shapes in Astrophysics and Related Topics)

4 pages, 207 KiB

Open AccessFeature PaperArticle

Correcting the Input Data for Calculating the Asymmetry of Hydrogenic Spectral Lines in Plasmas

by Paul Sanders and Eugene Oks

Atoms 2018, 6(1), 9; https://doi.org/10.3390/atoms6010009 - 06 Mar 2018

Cited by 2 | Viewed by 2603

Abstract

We provide corrections to the data in Sholin’s tables from his paper in Optics and Spectroscopy 26 (1969) 27. Since his data was used numerous times by various authors to calculate the asymmetry of hydrogenic spectral lines in plasmas, our corrections should motivate [...] Read more.

We provide corrections to the data in Sholin’s tables from his paper in Optics and Spectroscopy 26 (1969) 27. Since his data was used numerous times by various authors to calculate the asymmetry of hydrogenic spectral lines in plasmas, our corrections should motivate revisions of the previous calculations of the asymmetry and its comparison with the experimental asymmetry, and thus should have a practical importance. Full article

(This article belongs to the Special Issue Stark Broadening of Spectral Lines in Plasmas)

10 pages, 230 KiB

Open AccessFeature PaperArticle

The Effect of Correlation on Spectra of the Lanthanides: Pr³⁺

by Charlotte Froese Fischer and Gediminas Gaigalas

Atoms 2018, 6(1), 8; https://doi.org/10.3390/atoms6010008 - 25 Feb 2018

Cited by 6 | Viewed by 2897

Abstract

The effect of correlation on the spectra of lanthanide ions has been investigated using variational methods based on multiconfiguration Dirac–Hartree–Fock (MCDHF) theory. Results from several computational models are reported for Pr³⁺. The first assumes an inactive Cd-like

4 d^{10}

core [...] Read more.

The effect of correlation on the spectra of lanthanide ions has been investigated using variational methods based on multiconfiguration Dirac–Hartree–Fock (MCDHF) theory. Results from several computational models are reported for Pr³⁺. The first assumes an inactive Cd-like

4 d^{10}

core with valence electrons in

4 f^{2} 5 s^{2} 5 p^{6}

subshells. Additional models extend correlation to include core effects. It is shown that, with such models, the difference between computed energy levels and those from observed data increases with the energy of the level, suggesting that correlation among outer electrons should also be based on the correlated core of excited configuration state functions (CSFs). Some M1 transition probabilities are reported for the most accurate model and compared with predictions obtained from semi-empirical methods. Full article

(This article belongs to the Special Issue Current Developments and Applications of Atomic Structure and Radiative Process Investigations)

9 pages, 749 KiB

Open AccessArticle

Excitation of the 2S State of Atomic Hydrogen by Electron Impact

by Anand K. Bhatia

Atoms 2018, 6(1), 7; https://doi.org/10.3390/atoms6010007 - 12 Feb 2018

Cited by 8 | Viewed by 3130

Abstract

The excitation cross sections of the 2S state of atomic hydrogen at 10 low incident electron energies (10.30 and 54.5 eV) have been calculated using the variational polarized method. Nine partial waves are used to get convergence of cross sections in the [...] Read more.

The excitation cross sections of the 2S state of atomic hydrogen at 10 low incident electron energies (10.30 and 54.5 eV) have been calculated using the variational polarized method. Nine partial waves are used to get convergence of cross sections in the above energy range. The maximum of the cross section is 0.137

π a_{0}^{2}

at 11.14 eV which is close to the experimental result 0.163

\pm 0.2 π a_{0}^{2}

at 11.6

\pm

0.2 eV. The present results are compared with other calculations, many of them are based on the close-coupling approximation, including the R-matrix method. Differential cross sections at 13.6 eV incident energy have also been calculated. Spin-flip cross sections have been calculated and compared with those obtained using the close-coupling approximation. Full article

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6 pages, 272 KiB

Open AccessArticle

Contribution of Lienard-Wiechert Potential to the Electron Broadening of Spectral Lines in Plasmas

by Mohammed Tayeb Meftah, Khadra Arif, Keltoum Chenini, Kamel Ahmed Touati and Said Douis

Atoms 2018, 6(1), 6; https://doi.org/10.3390/atoms6010006 - 08 Feb 2018

Cited by 1 | Viewed by 3086

Abstract

Lienard-Wiechert or retarded electric and magnetic fields are produced by moving electric charges with respect to a rest frame. In hot plasmas, such fields may be created by high velocity free electrons. The resulting electric field has a relativistic expression that depends on [...] Read more.

Lienard-Wiechert or retarded electric and magnetic fields are produced by moving electric charges with respect to a rest frame. In hot plasmas, such fields may be created by high velocity free electrons. The resulting electric field has a relativistic expression that depends on the ratio of the free electron velocity to the speed of light in vacuum c. In this work, we consider the semi-classical dipole interaction between the emitter ions and the Lienard-Wiechert electric field of the free electrons and compute its contribution to the broadening of the spectral line shape in hot and dense plasmas. Full article

(This article belongs to the Special Issue Spectral Line Shapes in Astrophysics and Related Topics)

2 pages, 165 KiB

Open AccessEditorial

Acknowledgement to Reviewers of Atoms in 2017

by Atoms Editorial Office

Atoms 2018, 6(1), 5; https://doi.org/10.3390/atoms6010005 - 24 Jan 2018

Viewed by 2379

Abstract

Peer review is an essential part in the publication process, ensuring that Atoms maintains high quality standards for its published papers [...] Full article

8 pages, 280 KiB

Open AccessFeature PaperArticle

The Application of the Cut-Off Coulomb Model Potential for the Calculation of Bound-Bound State Transitions

by Nenad M. Sakan, Vladimir A. Srećković, Zoran J. Simić and Milan S. Dimitrijević

Atoms 2018, 6(1), 4; https://doi.org/10.3390/atoms6010004 - 12 Jan 2018

Cited by 1 | Viewed by 3164

Abstract

In this contribution, we present results of bound state transition modeling using the cut-off Coulomb model potential. The cut-off Coulomb potential has proven itself as a model potential for the dense hydrogen plasma. The main aim of our investigation include further steps of [...] Read more.

In this contribution, we present results of bound state transition modeling using the cut-off Coulomb model potential. The cut-off Coulomb potential has proven itself as a model potential for the dense hydrogen plasma. The main aim of our investigation include further steps of improvement of the usage of model potential. The results deal with partially ionized dense hydrogen plasma. The presented results covers

N_{e} = 6.5 \times 10^{18} {cm}^{- 3}

,

T = 18,000 K

and

N_{e} = 1.5 \times 10^{19} {cm}^{- 3}

,

T = 23,000 K,

where the comparison with the experimental data should take place, and the theoretical values for comparison. Since the model was successfully applied on continuous photoabsorption of dense hydrogen plasma in the broad area of temperatures and densities, it is expected to combine both continuous and bound-bound photoabsorption within single quantum mechanical model with the same success. Full article

(This article belongs to the Special Issue Spectral Line Shapes in Astrophysics and Related Topics)

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10 pages, 351 KiB

Open AccessFeature PaperArticle

Oriented Polar Molecules in a Solid Inert-Gas Matrix: A Proposed Method for Measuring the Electric Dipole Moment of the Electron

by A. C. Vutha, M. Horbatsch and E. A. Hessels

Atoms 2018, 6(1), 3; https://doi.org/10.3390/atoms6010003 - 05 Jan 2018

Cited by 38 | Viewed by 6533

Abstract

We propose a very sensitive method for measuring the electric dipole moment of the electron using polar molecules embedded in a cryogenic solid matrix of inert-gas atoms. The polar molecules can be oriented in the

\hat{z}

-direction by an applied electric field, [...] Read more.

We propose a very sensitive method for measuring the electric dipole moment of the electron using polar molecules embedded in a cryogenic solid matrix of inert-gas atoms. The polar molecules can be oriented in the

\hat{z}

-direction by an applied electric field, as has recently been demonstrated by Park et al. The trapped molecules are prepared into a state that has its electron spin perpendicular to

\hat{z}

, and a magnetic field along

\hat{z}

causes precession of this spin. An electron electric dipole moment

d_{e}

would affect this precession due to the up to 100 GV/cm effective electric field produced by the polar molecule. The large number of polar molecules that can be embedded in a matrix, along with the expected long coherence times for the precession, allows for the possibility of measuring

d_{e}

to an accuracy that surpasses current measurements by many orders of magnitude. Because the matrix can inhibit molecular rotations and lock the orientation of the polar molecules, it may not be necessary to have an electric field present during the precession. The proposed technique can be applied using a variety of polar molecules and inert gases, which, along with other experimental variables, should allow for careful study of systematic uncertainties in the measurement. Full article

(This article belongs to the Special Issue High Precision Measurements of Fundamental Constants)

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4691 KiB

Open AccessFeature PaperArticle

Proton Charge Radius from Electron Scattering

by Ingo Sick

Atoms 2018, 6(1), 2; https://doi.org/10.3390/atoms6010002 - 30 Dec 2017

Cited by 23 | Viewed by 5039

Abstract

The rms-radius R of the proton charge distribution is a fundamental quantity needed for precision physics. This radius, traditionally determined from elastic electron-proton scattering via the slope of the Sachs form factor

G_{e} (q^{2})

extrapolated to momentum transfer [...] Read more.

The rms-radius R of the proton charge distribution is a fundamental quantity needed for precision physics. This radius, traditionally determined from elastic electron-proton scattering via the slope of the Sachs form factor

G_{e} (q^{2})

extrapolated to momentum transfer

q^{2} = 0

, shows a large scatter. We discuss the approaches used to analyze the e-p data, partly redo these analyses in order to identify the sources of the discrepancies and explore alternative parameterizations. The problem lies in the model dependence of the parameterized

G (q)

needed for the extrapolation. This shape of

G (q

<

q_{m i n})

is closely related to the shape of the charge density

ρ (r)

at large radii r, a quantity that is ignored in most analyses. When using our physics knowledge about this large-r density together with the information contained in the high-q data, the model dependence of the extrapolation is reduced, and different parameterizations of the pre-2010 data yield a consistent value for

R = 0.887 \pm 0.012

fm. This value disagrees with the more precise value

0.8409 \pm 0.0004

fm determined from the Lamb shift in muonic hydrogen. Full article

(This article belongs to the Special Issue High Precision Measurements of Fundamental Constants)

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1490 KiB

Open AccessFeature PaperReview

Symmetric Atom–Atom and Ion–Atom Processes in Stellar Atmospheres

by Vladimir A. Srećković, Ljubinko M. Ignjatović and Milan S. Dimitrijević

Atoms 2018, 6(1), 1; https://doi.org/10.3390/atoms6010001 - 21 Dec 2017

Cited by 6 | Viewed by 3584

Abstract

We present the results of the influence of two groups of collisional processes (atom–atom and ion–atom) on the optical and kinetic properties of weakly ionized stellar atmospheres layers. The first type includes radiative processes of the photodissociation/association and radiative charge exchange, the second [...] Read more.

We present the results of the influence of two groups of collisional processes (atom–atom and ion–atom) on the optical and kinetic properties of weakly ionized stellar atmospheres layers. The first type includes radiative processes of the photodissociation/association and radiative charge exchange, the second one the chemi-ionisation/recombination processes with participation of only hydrogen and helium atoms and ions. The quantitative estimation of the rate coefficients of the mentioned processes were made. The effect of the radiative processes is estimated by comparing their intensities with those of the known concurrent processes in application to the solar photosphere and to the photospheres of DB white dwarfs. The investigated chemi-ionisation/recombination processes are considered from the viewpoint of their influence on the populations of the excited states of the hydrogen atom (the Sun and an M-type red dwarf) and helium atom (DB white dwarfs). The effect of these processes on the populations of the excited states of the hydrogen atom has been studied using the general stellar atmosphere code, which generates the model. The presented results demonstrate the undoubted influence of the considered radiative and chemi- ionisation/recombination processes on the optical properties and on the kinetics of the weakly ionized layers in stellar atmospheres. Full article

(This article belongs to the Special Issue Spectral Line Shapes in Astrophysics and Related Topics)

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Atoms, Volume 6, Issue 1 (March 2018) – 12 articles

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