Atoms doi: 10.3390/atoms6030035

Authors: Menahem Krief Alexander Feigel Doron Gazit

We present opacity calculations with the newly developed STAR code, which implements the Super-Transition-Array (STA), with various improvements. The model is used to calculate and analyze local thermodynamic equilibrium opacities of mid and high Z elements and of the solar interior plasma. We briefly review the underlying computational model and present calculations for iron and neodymium over a wide range of temperature and density.

]]>Atoms doi: 10.3390/atoms6020034

Authors: Guillaume Seguineaud Gen Motojima Yoshiro Narushima Motoshi Goto

A spectroscopic method for spatial resolution measurement in fuel pellet ablation clouds is being developed in the Large Helical Device (LHD). Spatial resolution is obtained thanks to optics that have a narrow, band-shaped field-of-view. The Stark-broadened H&beta; emission line of a deuterium pellet ablation cloud is isolated and analyzed with a spectral lineshape code. The electron density profile of the ablation cloud along its direction of elongation is derived through least squares fitting. The obtained profile is peaked and has a dip at its center which confirms what can be found in simulations. Moreover, the order of magnitudes for the derived electron densities are in agreement with what has already been found in the LHD.

]]>Atoms doi: 10.3390/atoms6020033

Authors: Alexander V. Demura

A review of studies of the electric-field influence on spectral lines is presented, beginning from the discovery of the Stark effect, and in particular focused on phenomena related to the effects of the plasma microfield non-uniformity.

]]>Atoms doi: 10.3390/atoms6020032

Authors: J. Colgan D. P. Kilcrease N. H. Magee M. E. Sherrill C. J. Fontes P. Hakel

In 2015 Los Alamos National Laboratory (LANL) released a new set of OPLIB opacity tables for the elements hydrogen through zinc. The new LANL opacities are publicly available via our website and are already in use by the astrophysics community. In this contribution, we discuss the extension of our opacity calculations to elements beyond zinc. Such calculations are motivated by potential industrial applications (for elements such as Sn) as well as available experimental data with which to compare our calculations (for Ge and Br). After a short outline of our method for computing opacities for these elements, we make comparisons to available experimental data and find good agreement. Future plans are briefly discussed.

]]>Atoms doi: 10.3390/atoms6020031

Authors: Joyce Guzik Christopher Fontes Chris Fryer

Opacity enhancements for stellar interior conditions have been explored to explain observed pulsation frequencies and to extend the pulsation instability region for B-type main-sequence variable stars. For these stars, the pulsations are driven in the region of the opacity bump of Fe-group elements at ∼200,000 K in the stellar envelope. Here we explore effects of opacity enhancements for the somewhat cooler main-sequence A-type stars, in which p-mode pulsations are driven instead in the second helium ionization region at ∼50,000 K. We compare models using the new LANL OPLIB vs. LLNL OPAL opacities for the AGSS09 solar mixture. For models of two solar masses and effective temperature 7600 K, opacity enhancements have only a mild effect on pulsations, shifting mode frequencies and/or slightly changing kinetic-energy growth rates. Increased opacity near the bump at 200,000 K can induce convection that may alter composition gradients created by diffusive settling and radiative levitation. Opacity increases around the hydrogen and 1st He ionization region (∼13,000 K) can cause additional higher-frequency p modes to be excited, raising the possibility that improved treatment of these layers may result in prediction of new modes that could be tested by observations. New or wider convective zones and higher convective velocities produced by opacity increases could also affect angular momentum transport during evolution. More work needs to be done to quantify the effects of opacity on the boundaries of the pulsation instability regions for A-type stars.

]]>Atoms doi: 10.3390/atoms6020030

Authors: Sylvie Sahal-Bréchot Evgeny Stambulchik Milan S. Dimitrijević Spiros Alexiou Bin Duan Véronique Bommier

The purpose of the Spectral Line Shapes in Plasmas (SLSP) code comparison workshop is to compare different computational and analytical methods, in order to pinpoint sources of disagreements, infer limits of applicability, and assess accuracy. The present paper reviews a part of the results of the third (2015) and fourth (2017) workshops related to isolated lines.

]]>Atoms doi: 10.3390/atoms6020029

Authors: Roshin Raj Sheeba Mohammed Koubiti Nelly Bonifaci Franck Gilleron Caroline Mossé Jean-Christophe Pain Joël Rosato Evgeny Stambulchik

Many spectroscopic diagnostics are routinely used as techniques to infer the plasma parameters from line emission spectra, but their accuracy depends on the numerical model or code used for the fitting process. However, the validation of a line shape code requires some steps: the comparison of the line shape code with other similar codes for some academic (simple) cases and then for more complex ones, the comparison of the fitting parameters obtained from the best fit of the experimental spectra with those obtained with other diagnostic techniques, and/or the comparison of the fitting parameters obtained by different codes to fit the same experimental data. Here we compare the profiles of the hydrogen Balmer &beta; line in helium plasma computed by five codes for a selected set of plasma parameters and we report on the plasma parameters inferred by each of them from the fitting to a number of experimental spectra measured in a helium corona discharge where the pressure was in the range of 1&ndash;5 bars.

]]>Atoms doi: 10.3390/atoms6020028

Authors: Claudio Mendoza

The revision of the standard Los Alamos opacities in the 1980&ndash;1990s by a group from the Lawrence Livermore National Laboratory (OPAL) and the Opacity Project (OP) consortium was an early example of collaborative big-data science, leading to reliable data deliverables (atomic databases, monochromatic opacities, mean opacities, and radiative accelerations) widely used since then to solve a variety of important astrophysical problems. Nowadays the precision of the OPAL and OP opacities, and even of new tables (OPLIB) by Los Alamos, is a recurrent topic in a hot debate involving stringent comparisons between theory, laboratory experiments, and solar and stellar observations in sophisticated research fields: the standard solar model (SSM), helio and asteroseismology, non-LTE 3D hydrodynamic photospheric modeling, nuclear reaction rates, solar neutrino observations, computational atomic physics, and plasma experiments. In this context, an unexpected downward revision of the solar photospheric metal abundances in 2005 spoiled a very precise agreement between the helioseismic indicators (the radius of the convection zone boundary, the sound-speed profile, and helium surface abundance) and SSM benchmarks, which could be somehow reestablished with a substantial opacity increase. Recent laboratory measurements of the iron opacity in physical conditions similar to the boundary of the solar convection zone have indeed predicted significant increases (30&ndash;400%), although new systematic improvements and comparisons of the computed tables have not yet been able to reproduce them. We give an overview of this controversy, and within the OP approach, discuss some of the theoretical shortcomings that could be impairing a more complete and accurate opacity accounting.

]]>Atoms doi: 10.3390/atoms6020027

Authors: Anand Bhatia

A number of formulations have been used to investigate scattering of low-energy electrons and positrons from various targets. The hybrid theory of scattering, which takes into account the short-range as well as the long-range correlations, and is variationally correct, is described in this article. This approach has been applied to calculate phase shifts for scattering of electrons and positrons, resonances in two-electron systems, photodetachment, and photoionization of two-electron systems. This approach has also been applied to calculate excitation of 2s state of atomic hydrogen by electron impact. In photoabsorption the target can be left in 2p state instead of 1s state, resulting in the emission of Lyman-alpha radiation. Cross sections for this process are also calculated.

]]>Atoms doi: 10.3390/atoms6020026

Authors: Jonathan Tennyson Sergei N. Yurchenko

The ExoMol project is dedicated to providing molecular line lists for exoplanet and other hot atmospheres. The ExoMol procedure uses a mixture of ab initio calculations and available laboratory data. The actual line lists are generated using variational nuclear motion calculations. These line lists form the input for opacity models for cool stars and brown dwarfs as well as for radiative transport models involving exoplanets. This paper is a collection of molecular opacities for 52 molecules (130 isotopologues) at two reference temperatures, 300 K and 2000 K, using line lists from the ExoMol database. So far, ExoMol line lists have been generated for about 30 key molecular species. Other line lists are taken from external sources or from our work predating the ExoMol project. An overview of the line lists generated by ExoMol thus far is presented and used to evaluate further molecular data needs. Other line lists are also considered. The requirement for completeness within a line list is emphasized and needs for further line lists discussed.

]]>Atoms doi: 10.3390/atoms6020025

Authors: Kanti M. Aggarwal

Energy levels, radiative rates and lifetimes are reported for F-like Sc XIII and Ne-like Sc XII and Y XXX for which the general-purpose relativistic atomic structure package (GRASP) has been adopted. For all three ions, limited data exist in the literature but comparisons have been made wherever possible to assess the accuracy of the calculations. In the present work, the lowest 102, 125 and 139 levels have been considered for the respective ions. Additionally, calculations have also been performed with the flexible atomic code (FAC) to (particularly) confirm the accuracy of energy levels.

]]>Atoms doi: 10.3390/atoms6020024

Authors: Chihiro Suzuki Fumihiro Koike Izumi Murakami Naoki Tamura Shigeru Sudo

We have systematically observed extreme ultraviolet (EUV) spectra from highly charged ions of nine lanthanide elements with atomic numbers from 60&ndash;70 in optically thin plasmas produced in the Large Helical Device (LHD). Discrete spectral features with isolated lines from relatively higher charge states around Cu-like ions are observed under high temperature conditions around 2 keV, while narrowed quasicontinuum features from charge states around Ag-like ions are observed under low temperature conditions below 1 keV. The positions of the lines and the quasicontinuum features systematically move to shorter wavelengths as the atomic number increases. The wavelengths of the main peaks in the quasicontinuum features agree well with those of singlet transitions of Pd-like ions reported previously. We have easily identified discrete spectral lines from Cu-like and Ag-like ions, some of which are experimentally identified for the first time in the LHD. Their wavelengths are compared with theoretical calculations using a GRASP family of atomic codes. The theoretical values are synthesized to the LHD experimental data for the cases of Ag- and Pd-like ions.

]]>Atoms doi: 10.3390/atoms6020023

Authors: Christine Stollberg Evgeny Stambulchik Bin Duan Marco A. Gigosos Diego González Herrero Carlos A. Iglesias Caroline Mossé

We report experimental determination of plasma-induced Stark widths and shifts of the He II P &alpha; line and a comparison of the results with calculations performed by several computational approaches. The measurements were carried out in a small compressing plasma channel device, reaching electron densities in excess of 10 18 cm &minus; 3 and temperatures of a few eV. The experimental data are in a good agreement with some previously published studies. However, the measured relation between the Stark shift and width could not be reproduced by either of the codes, and this disagreement is not yet resolved. This suggests the existence of an additional effect that is not accounted for in the present models and leads to a larger than expected Stark shift of the He II P &alpha; line.

]]>Atoms doi: 10.3390/atoms6020022

Authors: Thomas Gomez Taisuke Nagayama Chris Fontes Dave Kilcrease Stephanie Hansen Mike Montgomery Don Winget

Atomic structure of N-electron atoms is often determined by solving the Hartree-Fock equations, which are a set of integro-differential equations. The integral part of the Hartree-Fock equations treats electron exchange, but the Hartree-Fock equations are not often treated as an integro-differential equation. The exchange term is often approximated as an inhomogeneous or an effective potential so that the Hartree-Fock equations become a set of ordinary differential equations (which can be solved using the usual shooting methods). Because the Hartree-Fock equations are an iterative-refinement method, the inhomogeneous term relies on the previous guess of the wavefunction. In addition, there are numerical complications associated with solving inhomogeneous differential equations. This work uses matrix methods to solve the Hartree-Fock equations as an integro-differential equation. It is well known that a derivative operator can be expressed as a matrix made of finite-difference coefficients; energy eigenvalues and eigenvectors can be obtained by using linear-algebra packages. The integral (exchange) part of the Hartree-Fock equation can be approximated as a sum and written as a matrix. The Hartree-Fock equations can be solved as a matrix that is the sum of the differential and integral matrices. We compare calculations using this method against experiment and standard atomic structure calculations. This matrix method can also be used to solve for free-electron wavefunctions, thus improving how the atoms and free electrons interact. This technique is important for spectral line broadening in two ways: it improves the atomic structure calculations, and it improves the motion of the plasma electrons that collide with the atom.

]]>Atoms doi: 10.3390/atoms6020021

Authors: Paul Sanders Eugene Oks

There was previously proposed and experimentally implemented a new diagnostic method for measuring the electron density Ne using the asymmetry of hydrogenic spectral lines in dense plasmas. Compared to the traditional method of deducing Ne from the experimental widths of spectral lines, the new method has the following advantages. First, the traditional method requires measuring widths of at least two spectral lines (to isolate the Stark broadening from competing broadening mechanisms), while for the new diagnostic method it is sufficient to obtain the experimental profile of just one spectral line. Second, the traditional method would be difficult to implement if the center of the spectral lines was optically thick, while the new diagnostic method could still be used even in this case. In the theory underlying this new diagnostic method, the contribution of plasma ions to the spectral line asymmetry was calculated only for configurations where the perturbing ions were outside the bound electron cloud of the radiating atom/ion (non-penetrating configurations). In the present paper, we take into account the contribution to the spectral line asymmetry from penetrating configurations, where the perturbing ion is inside the bound electron cloud of the radiating atom/ion. We show that in high-density plasmas, the allowance for penetrating ions can result in significant corrections to the electron density deduced from the spectral line asymmetry.

]]>Atoms doi: 10.3390/atoms6020020

Authors: Rihab Aloui Haykel Elabidi Sylvie Sahal-Bréchot Milan S. Dimitrijević

We present in this paper the results of a theoretical study of electron impact broadening for several lines of the Ar VII ion. The results have been obtained using our quantum mechanical method and the semiclassical perturbation one. Results are presented for electron density 1018 cm&minus;3 and for electron temperatures ranging from 2 &times; 10 4 to 5 &times; 10 5 K required for plasma modeling. Our results have been compared to other semiclassical ones obtained using different sources of atomic data. A study of the strong collisions contributions to line broadening has been performed. The atomic structure and collision data used for the calculations of line broadening are also calculated by our codes and compared to available theoretical results. The agreement found between the two calculations ensures that our line broadening procedure uses adequate structure and collision data.

]]>Atoms doi: 10.3390/atoms6020019

Authors: Roshin Raj Sheeba Mohammed Koubiti Nelly Bonifaci Franck Gilleron Jean-Christophe Pain Evgeny Stambulchik

Passive plasma spectroscopy is a well-established non-intrusive diagnostic technique. Depending on the emitter and its environment which determine the dominant interactions and effects governing emission line shapes, passive spectroscopy allows the determination of electron densities, emitter and perturber temperatures, as well as other quantities like relative abundances. However, using spectroscopy requires appropriate line shape codes retaining all the physical effects governing the emission line profiles. This is required for line shape code developers to continuously correct or improve them to increase their accuracy when applied for diagnostics. This is exactly the aim expected from code&ndash;code and code&ndash;data comparisons. In this context, the He i 492 nm line emitted in a helium corona discharge at room temperature represents an ideal case since its profile results from several broadening mechanisms: Stark, Doppler, resonance, and van der Waals. The importance of each broadening mechanism depends on the plasma parameters. Here the profiles of the He i 492 nm in a helium plasma computed by various codes are compared for a selected set of plasma parameters. In addition, preliminary results related to plasma parameter determination using an experimental spectrum from a helium corona discharge at atmospheric pressure, are presented.

]]>Atoms doi: 10.3390/atoms6020018

Authors: Renat Sultanov Dennis Guster Sadhan Adhikari

The influence of an additional strong p ¯ -p nuclear interaction in a three-charge-particle system with arbitrary masses is investigated. Specifically, the system of p ¯ , μ − , and p is considered in this paper, where p ¯ is an antiproton, μ − is a muon and p is a proton. A numerical computation in the framework of a detailed few-body approach is carried out for the following protonium (antiprotonic hydrogen) formation three-body reaction: p ¯ + H μ ( 1 s ) → ( p ¯ p ) α + μ − . Here, H μ ( 1 s ) is a ground state muonic hydrogen, i.e., a bound state of p and μ − . A bound state of p and its antimatter counterpart p ¯ is a protonium atom in a quantum atomic state α , i.e., P n = ( p ¯ p ) α . The low-energy cross sections and rates of the P n formation reaction are computed in the framework of coupled Faddeev-Hahn-type equations. The strong p ¯ -p interaction is included in these calculations within a first order approximation. It was found, that the inclusion of the nuclear interaction results in a quite significant correction to the rate of the three-body reaction.

]]>Atoms doi: 10.3390/atoms6020017

Authors: Aldo Antognini Daniel Kaplan Klaus Kirch Andreas Knecht Derrick Mancini James Phillips Thomas Phillips Robert Reasenberg Thomas Roberts Anna Soter

The gravitational acceleration of antimatter, g ¯ , has yet to be directly measured; an unexpected outcome of its measurement could change our understanding of gravity, the universe, and the possibility of a fifth force. Three avenues are apparent for such a measurement: antihydrogen, positronium, and muonium, the last requiring a precision atom interferometer and novel muonium beam under development. The interferometer and its few-picometer alignment and calibration systems appear feasible. With 100 nm grating pitch, measurements of g ¯ to 10%, 1%, or better can be envisioned. These could constitute the first gravitational measurements of leptonic matter, of 2nd-generation matter, and possibly, of antimatter.

]]>Atoms doi: 10.3390/atoms6020016

Authors: Mohammed Tayeb Meftah Hadda Gossa Kamel Ahmed Touati Keltoum Chenini Amel Naam

In this work, we report some relativistic effects on the spectral line broadening. In particular, we give a new Doppler broadening in extra hot plasmas that takes into account the possible high velocity of the emitters. This suggests the use of an appropriate distribution of the velocities for the emitters. Indeed, the Juttner-Maxwell distribution of the velocities is more adequate for relativistic velocities of the emitters when the latter are in plasma with an extra high temperature. We find an asymmetry in the Doppler line shapes unlike the case of the traditional Doppler effect.

]]>Atoms doi: 10.3390/atoms6020015

Authors: Milan Dimitrijević Abhishek Chougule

Using the modified semiempirical method of Dimitrijević and Konjević, Stark widths have been calculated for six Cr III transitions, for an electron density of 10 17 cm ‒ 3 and for temperatures from 5000–80,000 K. Results have been used for the investigation of the influence of Stark broadening on spectral lines in cool DO white dwarf atmospheres. Calculated Stark widths will be implemented in the STARK-B database, which is also a part of the Virtual Atomic and Molecular Data Center (VAMDC).

]]>Atoms doi: 10.3390/atoms6020014

Authors: Eugene Oks

We analytically calculated the shift of spectral lines of hydrogenlike ions for non-spherical nuclear shapes, such as the oblate or prolate ellipsoid of revolution. We show that the allowance for the ellipsoidal nuclear shape can change the shift of spectral lines of muonic hydrogenlike ions by several times compared to the corresponding shift for spherical nuclei. This can serve as an additional method for the experimental determination of the quadrupole moment of nuclei and of the standard beta-parameter related to the quadrupole moment.

]]>Atoms doi: 10.3390/atoms6020013

Authors: Spiros Alexiou Evgeny Stambulchik Thomas Gomez Mohammed Koubiti

For a given set of plasma parameters, along a single series (Lyman, Balmer, etc.) the lines with higher principal quantum number (n) lines get progressively wider, closer to each other, and start merging for a certain critical n. In the present work, four different codes (with further options) are used to calculate the entire Balmer series for moderate and high electron densities. Particular attention is paid to the relevant physics, such as the cutoff criteria, strong and penetrating electron collisions.

]]>Atoms doi: 10.3390/atoms6010012

Authors: J. Rosato S. Ferri R. Stamm

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.

]]>Atoms doi: 10.3390/atoms6010011

Authors: Franck Gilleron Jean-Christophe Pain

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.

]]>Atoms doi: 10.3390/atoms6010010

Authors: Milan Dimitrijević Zoran Simić Roland Stamm Joël Rosato Nenad Milovanović Cristina Yubero

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).

]]>Atoms doi: 10.3390/atoms6010009

Authors: Paul Sanders Eugene Oks

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.

]]>Atoms doi: 10.3390/atoms6010008

Authors: Charlotte Froese Fischer Gediminas Gaigalas

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.

]]>Atoms doi: 10.3390/atoms6010007

Authors: Anand Bhatia

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 ± 0.2 π a 0 2 at 11.6 ± 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.

]]>Atoms doi: 10.3390/atoms6010006

Authors: Mohammed Meftah Khadra Arif Keltoum Chenini Kamel Touati Said Douis

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.

]]>Atoms doi: 10.3390/atoms6010005

Authors: Atoms Editorial Office

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

]]>Atoms doi: 10.3390/atoms6010004

Authors: Nenad Sakan Vladimir Srećković Zoran Simić Milan Dimitrijević

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 × 10 18 cm − 3 , T = 18,000 K and N e = 1.5 × 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.

]]>Atoms doi: 10.3390/atoms6010003

Authors: A. Vutha M. Horbatsch E. Hessels

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 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 z ^ , and a magnetic field along 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.

]]>Atoms doi: 10.3390/atoms6010002

Authors: Ingo Sick

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 &lt; 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 ± 0.012 fm. This value disagrees with the more precise value 0.8409 ± 0.0004 fm determined from the Lamb shift in muonic hydrogen.

]]>Atoms doi: 10.3390/atoms6010001

Authors: Vladimir Srećković Ljubinko Ignjatović Milan Dimitrijević

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.

]]>Atoms doi: 10.3390/atoms5040050

Authors: Dmitry Efimov Martins Bruvelis Nikolai Bezuglov Milan Dimitrijević Andrey Klyucharev Vladimir Srećković Yurij Gnedin Francesco Fuso

The time-dependent population dynamics of hyperfine (HF) sublevels of n 2 p 3 / 2 atomic states upon laser excitation in a cold medium of alkali atoms is examined. We demonstrate some peculiarities of the absorption HF multiplet formation in D2-line resulting from a long interaction time (∼200 μ s) interaction between light and Na ( n = 3 ) and Cs ( n = 6 ) atoms in a cold and slow sub-thermal ( T ∼ 1 K) beam. We analytically describe a number of D2-line-shape effects that are of interest in spectroscopic studies of cold dusty white dwarfs: broadening by optical pumping, intensity redistribution within components of D2-line HF multiplet for partially closed transitions and asymmetry of absorption lines induced by AC Stark shifts for cyclic transitions.

]]>Atoms doi: 10.3390/atoms5040049

Authors: Zlatko Majlinger Milan Dimitrijević Zoran Simić

Regularities and systematic trends among the Stark widths of 18 Zr IV spectral lines obtained by modified semiempirical approach have been discussed. Also we compared those calculated Stark broadening parameters with estimates according to Cowley, Purić et al. and Purić and Šćepanović and checked the possibility to find some new estimates. It is demonstrated as well that the formula of Cowley (1971) overestimates Stark widths, obtained by using modified semiempirical method, with the increase of angular orbital momentum quantum number due to its neglection. It is also found that the results obtained by using formula for simple estimates of Purić et al. (1991) are in agreement with the modified semiempirical results within the estimated error bars of both methods, while the estimates using formula of Purić and Šćepanović (1999) are in strong disagreement which increases with the increase of angular orbital momentum quantum number.

]]>Atoms doi: 10.3390/atoms5040048

Authors: Ulrich Jentschura Chandra Adhikari

The collisional shift of a transition constitutes an important systematic effect in high-precision spectroscopy. Accurate values for van der Waals interaction coefficients are required in order to evaluate the distance-dependent frequency shift. We here consider the interaction of excited hydrogen 6 P atoms with metastable atoms (in the 2 S state), in order to explore the influence of quasi-degenerate 2 P and 6 S states on the dipole-dipole interaction. The motivation for the calculation is given by planned high-precision measurements of the transition. Due to the presence of quasi-degenerate levels, one can use the non-retarded approximation for the interaction terms over wide distance ranges.

]]>Atoms doi: 10.3390/atoms5040047

Authors: Alexander Ryabtsev Rimma Kildiyarova Edward Kononov

The spectrum of tin, excited in a vacuum spark, was recorded in the region 500–1131 Å on a 6.65-m normal incidence spectrograph. The transitions between 4d85s, 4d86s, 4d85p and 4d85d excited configurations in Sn VI were studied. More than 500 lines of the 4d85p–4d85d and 4d85p–4d86s were identified with the aid of the Cowan code calculations. 67 energy levels (out of 70 possible levels of the 4d85d configuration) and all but two 4d86s levels were found. The wavelength of the 4d85s–4d85p transitions in the region 839–1131 Å were re-measured and supplemented by Sn VI lines in the region 1131–1300 Å measured previously by Srivastava et al. (1977) for optimisation of the energy level values. The SnVI line list in the region 500–1300 Å contains now 741 lines with calculated transition probabilities.

]]>Atoms doi: 10.3390/atoms5040046

Authors: Bratislav Marinković Jan Bredehöft Veljko Vujčić Darko Jevremović Nigel Mason

The emission of [O I] lines in the coma of Comet 67P/Churyumov-Gerasimenko during the Rosetta mission have been explained by electron impact dissociation of water rather than the process of photodissociation. This is the direct evidence for the role of electron induced processing has been seen on such a body. Analysis of other emission features is handicapped by a lack of detailed knowledge of electron impact cross sections which highlights the need for a broad range of electron scattering data from the molecular systems detected on the comet. In this paper, we present an overview of the needs for electron scattering data relevant for the understanding of observations in coma, the tenuous atmosphere and on the surface of 67P/Churyumov-Gerasimenko during the Rosetta mission. The relevant observations for elucidating the role of electrons come from optical spectra, particle analysis using the ion and electron sensors and mass spectrometry measurements. To model these processes electron impact data should be collated and reviewed in an electron scattering database and an example is given in the BEAMD, which is a part of a larger consortium of Virtual Atomic and Molecular Data Centre—VAMDC.

]]>Atoms doi: 10.3390/atoms5040045

Authors: Sergey Kotov Sergey Dodonov

We present the first results of medium-band photometric observations on the 1m Schmidt Telescope of Byurakan Astrophysical Observatory (Armenia). The object sample was created in the SA68 field. The medium-band filter set (13 filters with FWHM = 250 Å + 5 broadband SDSS filters) allowed us to create low-resolution spectra of each object in the SA68 field. We compared them with the template spectra to select AGNs and to determine their photometric redshifts. Our sample consists of 330 objects with 0.5–5.1 redshift range and complete up to 23.0 AB magnitude. The comparison of our sample with SDSS DR10 and BOSS + MMT QSO showed that sufficiently more objects in the 3.2–5.1 redshift range were found.

]]>Atoms doi: 10.3390/atoms5040044

Authors: Ny Kieu Joël Rosato Roland Stamm Jelena Kovačević-Dojcinović Milan Dimitrijević Luka Popović Zoran Simić

White dwarfs with magnetic field strengths larger than 10 T are understood to represent more than 10% of the total population of white dwarfs. The presence of such strong magnetic fields is clearly indicated by the Zeeman triplet structure visible on absorption lines. In this work, we discuss the line broadening mechanisms and focus on the sensitivity of hydrogen lines on the magnetic field. We perform new calculations in conditions relevant to magnetized DA stellar atmospheres using models inspired from magnetic fusion plasma spectroscopy. A white dwarf spectrum from the Sloan Digital Sky Survey (SDSS) database is analyzed. An effective temperature is provided by an adjustment of the background radiation with a Planck function, and the magnetic field is inferred from absorption lines presenting a Zeeman triplet structure. An order-of-magnitude estimate for the electron density is also performed from Stark broadening analysis.

]]>Atoms doi: 10.3390/atoms5040043

Authors: Giovanni La Mura Marco Berton Sina Chen Abhishek Chougule Stefano Ciroi Enrico Congiu Valentina Cracco Michele Frezzato Sabrina Mordini Piero Rafanelli

The spectra of active galactic nuclei (AGNs) are often characterized by a wealth of emission lines with different profiles and intensity ratios that lead to a complicated classification. Their electromagnetic radiation spans more than 10 orders of magnitude in frequency. In spite of the differences between various classes, the origin of their activity is attributed to a combination of emitting components, surrounding an accreting supermassive black hole (SMBH), in the unified model. Currently, the execution of sky surveys, with instruments operating at various frequencies, provides the possibility to detect and to investigate the properties of AGNs on very large statistical samples. As a result of the spectroscopic surveys that allow the investigation of many objects, we have the opportunity to place new constraints on the nature and evolution of AGNs. In this contribution, we present the results obtained by working on multi-frequency data, and we discuss their relations with the available optical spectra. We compare our findings with the AGN unified model predictions, and we present a revised technique to select AGNs of different types from other line-emitting objects. We discuss the multi-frequency properties in terms of the innermost structures of the sources.

]]>Atoms doi: 10.3390/atoms5040042

Authors: Ljubinko Ignjatović Vladimir Srećković Milan Dimitrijević

As the object of investigation, astrophysical fully ionized electron-ion plasma is chosen with positively charged ions of two different kinds, including the plasmas of higher non-ideality. The direct aim of this work is to develop, within the problem of finding the mean potential energy of the charged particle for such plasma, a new model, self-consistent method of describing the electrostatic screening. Within the presented method, such extremely significant phenomena as the electron-ion and ion-ion correlations are included in the used model. We wish to draw attention to the fact that the developed method is suitable for astrophysical applications. Here we keep in mind that in outer shells of stars, the physical conditions change from those that correspond to the rare, practically ideal plasma, to those that correspond to extremely dense non-ideal plasma.

]]>Atoms doi: 10.3390/atoms5040040

Authors: Roman Venger Tetiana Tmenova Flavien Valensi Anatoly Veklich Yann Cressault Viacheslav Boretskij

A phenomenological picture of pulsed electrical discharge in water is produced by combining electrical, spectroscopic, and imaging methods. The discharge is generated by applying ~350 μs long 100 to 220 V pulses (values of current from 400 to 1000 A, respectively) between the point-to-point copper electrodes submerged into the non-purified tap water. Plasma channel and gas bubble occur between the tips of the electrodes, which are initially in contact with each other. The study includes detailed experimental investigation of plasma parameters of such discharge using the correlation between time-resolved high-speed imaging, electrical characteristics, and optical emission spectroscopic data. Radial distributions of the electron density of plasma is estimated from the analysis of profiles and widths of registered Hα and Hβ hydrogen lines, and Cu I 515.3 nm line, exposed to the Stark mechanism of spectral lines’ broadening. Estimations of the electrodes’ erosion rate and bubbles’ size depending on the electrical input parameters of the circuit are presented. Experimental results of this work may be valuable for the advancement of modeling and the theoretical understanding of the pulse electric discharges in water.

]]>Atoms doi: 10.3390/atoms5040041

Authors: Cristina Yubero Antonio Rodero Milan Dimitrijevic Antonio Gamero Maria García

The spectroscopic method for gas temperature determination in argon non-thermal plasmas sustained at atmospheric pressure proposed recently by Spectrochimica Acta Part B 129 14 (2017)—based on collisional broadening measurements of selected pairs of argon atomic lines, has been applied to other pairs of argon atomic lines, and the discrepancies found in some of these results have been analyzed. For validation purposes, the values of the gas temperature obtained using the different pairs of lines have been compared with the rotational temperatures derived from the OH ro-vibrational bands, using the Boltzmann-plot technique.

]]>Atoms doi: 10.3390/atoms5040039

Authors: Elena Shablovinskaya

Among the great number of controversial issues, the most topical one both for theoretical and observational astrophysics presently is a problem of active galactic nuclei investigation. To explain the behaviour of blazar AO 0235+164, which has been under observation at the LX200 telescope (SPbSU) since 2002, the method of analyzing developed by V.A. Hagen-Thorn and S.G. Marchenko was applied. It is based on the assumption that in the case of observational data lying on the straight line in the absolute Stokes parameters space { I , Q , U } (for polarimetry) and the fluxes space { F 1 , . . F n } (for photometry), relative Stokes parameters and relative flux ratios stay unchanged , and consequently, only one source is corresponding to the variability of general value of flux. In this paper, the photometric and polarimetric interpretation of blazar behaviour is presented. Furthermore, the flux and flux–flux diagrams are obtained for three periods of object monitoring: 2006–2007 and 2008–2009 (outbursts) and 2009–2016 (decline with 2015 outburst).

]]>Atoms doi: 10.3390/atoms5040038

Authors: Florin Constantin

A double resonance two-photon spectroscopy scheme is discussed to probe jointly rotational and rovibrational transitions of ensembles of trapped HD+ ions. The two-photon transition rates and lightshifts are calculated with the two-photon tensor operator formalism. The rotational lines may be observed with sub-Doppler linewidth at the hertz level and good signal-to-noise ratio, improving the resolution in HD+ spectroscopy beyond the 10−12 level. The experimental accuracy, estimated at the 10−12 level, is comparable with the accuracy of theoretical calculations of HD+ energy levels. An adjustment of selected rotational and rovibrational HD+ lines may add clues to the proton radius puzzle, may provide an independent determination of the Rydberg constant, and may improve the values of proton-to-electron and deuteron-to-proton mass ratios beyond the 10−11 level.

]]>Atoms doi: 10.3390/atoms5040037

Authors: Kanti Aggarwal

The analysis and modelling of a range of plasmas (for example, astrophysical, laser- produced and fusion) require atomic data for a number of parameters, such as energy levels, radiative rates and electron impact excitation rates, or equivalently, the effective collision strengths. Such data are desired for a wide range of elements and their many ions, although all elements are not useful for all types of plasmas. Since measurements of atomic data are mostly confined to only a few energy levels of some ions, calculations for all parameters are highly important. However, often, there are large discrepancies among different calculations for almost all parameters, which makes it difficult to apply the data with confidence. Many such discrepancies (and the possible remedies) were discussed earlier (Fusion Sci. Technol. 2013, 63, 363). Since then, many more anomalies for almost all of these atomic parameters have been noticed. Therefore, this paper is a revisit of various atomic parameters to highlight the large discrepancies, their possible sources and some suggestions to avoid these, so that comparatively more accurate and reliable atomic data may be available in the future.

]]>Atoms doi: 10.3390/atoms5040036

Authors: Joël Rosato Ny Kieu Ibtissem Hannachi Mohammed Koubiti Yannick Marandet Roland Stamm Milan S. Dimitrijević Zoran Simić

The shape of atomic spectral lines in plasmas contains information on the plasma parameters, and can be used as a diagnostic tool. Under specific conditions, the plasma located at the edge of tokamaks has parameters similar to those in magnetic white dwarf stellar atmospheres, which suggests that the same line shape models can be used. A problem common to tokamak and magnetic white dwarfs concerns the modeling of Stark broadening of hydrogen lines in the presence of an external magnetic field and the related Zeeman effect. In this work, we focus on a selection of issues relevant to Stark broadening in magnetized hydrogen plasmas. Various line shape models are presented and discussed through applications to ideal cases.

]]>Atoms doi: 10.3390/atoms5040035

Authors: Joël Rosato Nelly Bonifaci Zhiling Li Roland Stamm

We present an analysis of spectra observed in a corona discharge designed for the study of dielectrics in electrical engineering. The medium is a gas of helium and the discharge was performed at the vicinity of a tip electrode under high voltage. The shape of helium lines is dominated by the Stark broadening due to the plasma microfield. Using a computer simulation method, we examine the sensitivity of the He 492 nm line shape to the electron density. Our results indicate the possibility of a density diagnostic based on passive spectroscopy. The influence of collisional broadening due to interactions between the emitters and neutrals is discussed.

]]>Atoms doi: 10.3390/atoms5040034

Authors: Ibtissem Hannachi Mutia Meireni Paul Génésio Joël Rosato Roland Stamm Yannick Marandet

We look at the effect of wave collapse turbulence on a hydrogen line shape in plasma. An atom immersed in plasma affected by strong Langmuir turbulence may be perturbed by a sequence of wave packets with a maximum electric field magnitude that is larger than the Holtsmark field. For such conditions, we propose to calculate the shape of the hydrogen Lyman α Lyman β and Balmer α lines with a numerical integration of the Schrödinger equation coupled to a simulation of a sequence of electric fields modeling the effects of the Langmuir wave. We present and discuss several line profiles of Lyman and Balmer lines.

]]>Atoms doi: 10.3390/atoms5030033

Authors: Paola Marziani Ascensión Olmo Mary Martínez-Aldama Deborah Dultzin Alenka Negrete Edi Bon Natasa Bon Mauro D’Onofrio

Can high ionization lines such as CIV λ 1549 provide useful virial broadening estimators for computing the mass of the supermassive black holes that power the quasar phenomenon? The question has been dismissed by several workers as a rhetorical one because blue-shifted, non-virial emission associated with gas outflows is often prominent in CIV λ 1549 line profiles. In this contribution, we first summarize the evidence suggesting that the FWHM of low-ionization lines like H β and MgII λ 2800 provide reliable virial broadening estimators over a broad range of luminosity. We confirm that the line widths of CIV λ 1549 is not immediately offering a virial broadening estimator equivalent to the width of low-ionization lines. However, capitalizing on the results of Coatman et al. (2016) and Sulentic et al. (2017), we suggest a correction to FWHM CIV λ 1549 for Eddington ratio and luminosity effects that, however, remains cumbersome to apply in practice. Intermediate ionization lines (IP ∼ 20–30 eV; AlIII λ 1860 and SiIII] λ 1892) may provide a better virial broadening estimator for high redshift quasars, but larger samples are needed to assess their reliability. Ultimately, they may be associated with the broad-line region radius estimated from the photoionization method introduced by Negrete et al. (2013) to obtain black hole mass estimates independent from scaling laws.

]]>Atoms doi: 10.3390/atoms5030032

Authors: Roland Stamm Ibtissem Hannachi Mutia Meireni Laurence Godbert-Mouret Mohammed Koubiti Yannick Marandet Joël Rosato Milan Dimitrijević Zoran Simić

Impact approximation is widely used for calculating Stark broadening in a plasma. We review its main features and different types of models that make use of it. We discuss recent developments, in particular a quantum approach used for both the emitter and the perturbers. Numerical simulations are a useful tool for gaining insight into the mechanisms at play in impact-broadening conditions. Our simple model allows the integration of the Schrödinger equation for an emitter submitted to a fluctuating electric field. We show how we can approach the impact results, and how we can investigate conditions beyond the impact approximation. The simple concepts developed in impact and simulation approaches enable the analysis of complex problems such as the effect of plasma rogue waves on hydrogen spectra.

]]>Atoms doi: 10.3390/atoms5030031

Authors: Vladimir Srećković Ljubinko Ignjatović Darko Jevremović Veljko Vujčić Milan Dimitrijević

Spectroscopy has been crucial for our understanding of physical and chemical phenomena. The interpretation of interstellar line spectra with radiative transfer calculations usually requires two kinds of molecular input data: spectroscopic data (such as energy levels, statistical weights, transition probabilities, etc.) and collision data. This contribution describes how such data are collected, stored, and which limitations exist. Also, here we summarize challenges of atomic/molecular databases and point out our experiences, problems, etc., which we are faced with. We present overview of future developments and needs in the areas of radiative transfer and molecular data.

]]>Atoms doi: 10.3390/atoms5030029

Authors: Milan Dimitrijević Zoran Simić Aleksandar Valjarević Cristina Yubero

Sodium is a very important element for the research and analysis of astrophysical, laboratory, and technological plasmas, but neither theoretical nor experimental data on Stark broadening of Na IV spectral lines are present in the literature. Using the modified semiempirical method of Dimitrijević and Konjević, here Stark widths have been calculated for nine Na IV transitions. Na IV belongs to the oxygen isoelectronic sequence, and we have calculated Stark widths belonging to singlets, triplets, and quintuplets, as well as with different parent terms. This is used to discuss similarities within one transition array with different multiplicities and parent terms. Additionally, calculated widths will be implemented in the STARK-B database (http://stark-b.obspm.fr) which is also a part of the Virtual Atomic and Molecular Data Center (VAMDC—http://www.vamdc.org/).

]]>Atoms doi: 10.3390/atoms5030030

Authors: Roshani Silwal Endre Takacs Joan Dreiling John Gillaspy Yuri Ralchenko

Extreme ultraviolet spectra of the L-shell ions of highly charged yttrium (Y 26 + –Y 36 + ) were observed in the electron beam ion trap of the National Institute of Standards and Technology using a flat-field grazing-incidence spectrometer in the wavelength range of 4 nm-20 nm. The electron beam energy was systematically varied from 2.3 keV–6.0 keV to selectively produce different ionization stages. Fifty-nine spectral lines corresponding to Δ n = 0 transitions within the n = 2 and n = 3 shells have been identified using detailed collisional-radiative (CR) modeling of the non-Maxwellian plasma. The uncertainties of the wavelength determinations ranged between 0.0004 nm and 0.0020 nm. Li-like resonance lines, 2s– 2 p 1 / 2 and 2s–2 p 3 / 2 , and the Na-like D lines, 3s– 3 p 1 / 2 and 3s– 3 p 3 / 2 , have been measured and compared with previous measurements and calculations. Forbidden magnetic dipole (M1) transitions were identified and analyzed for their potential applicability in plasma diagnostics using large-scale CR calculations including approximately 1.5 million transitions. Several line ratios were found to show strong dependence on electron density and, hence, may be implemented in the diagnostics of hot plasmas, in particular in fusion devices.

]]>Atoms doi: 10.3390/atoms5030028

Authors: Saturnin Enzonga Yoca Pascal Quinet

A new set of radiative decay parameters (oscillator strengths, transition probabilities) for spectral lines in triply ionized thulium (Tm IV) has been obtained within the framework of the pseudo-relativistic Hartree-Fock (HFR) approach. The effects of configuration interaction and core-polarization have been investigated in detail and the quality of the results has been assessed through a comparison between different HFR physical models. The spectroscopic data listed in the present paper cover electric dipole as well as magnetic dipole and electric quadrupole transitions in a wide range of wavelengths from extreme ultraviolet to near infrared.

]]>Atoms doi: 10.3390/atoms5030027

Authors: Milan Dimitrijević Aleksandar Valjarević Sylvie Sahal-Bréchot

Using the semi-classical perturbation approach in the impact approximation, full width at half maximum and shift have been determined for eight spectral lines of Ar VII, for broadening by electron-, proton-, and He III-impacts. The results are provided for temperatures from 20,000 K to 500,000 K, and for an electron density of 10 18 cm − 3 . The obtained results will be included in the STARK-B database, which is also in the virtual atomic and molecular data center (VAMDC).

]]>Atoms doi: 10.3390/atoms5030026

Authors: Rafik Hamdi Nabil Ben Nessib Sylvie Sahal Bréchot Milan Dimitrijević

Stark broadening parameters are of interest for many problems in astrophysics and laboratory plasmas investigation. Ar II spectral lines are observed in many kinds of stellar atmospheres such as the atmospheres of B-Type stars and subdwarf B stars. In this work, we present theoretical Stark widths for Ar II spectral lines. We use the impact semiclassical perturbation approach. Our results are compared with the available experimental values. Finally, the importance of the Stark broadening mechanism is studied in atmospheric conditions of subdwarf B stars.

]]>Atoms doi: 10.3390/atoms5030025

Authors: Elena Ivanova

The energies for the lower 3d3/24d3/2 [J = 1] and upper 3d3/24f5/2 [J = 1] working levels in the self-photopumped X-ray laser are analyzed along the Ni-like sequence. We have found some irregularities in these energy levels in the range Z = 42–49. The causes of the irregularities are studied. The list of elements that lase on the self-photopumped transition can be extended much further than originally known. We calculate the wavelengths of this transition in Ni-like sequence to Z = 79 using the relativistic perturbation theory with a zero approximation model potential. We estimate the wavelength accuracy for Z &gt; 50 as Δλ/λ ≤ 0.005.

]]>Atoms doi: 10.3390/atoms5030024

Authors: Ali Meftah Mourad Sabri Jean-François Wyart Wan-Ü Tchang-Brillet

In an attempt to improve U II analysis, the lowest configurations of both parities have been interpreted by means of the Racah-Slater parametric method, using Cowan codes. In the odd parity, including the ground state, 253 levels of the interacting configurations 5 f 3 7 s 2 + 5 f 3 6 d 7 s + 5 f 3 6 d 2 + 5 f 4 7 p + 5 f 5 are interpreted by 24 free parameters and 64 constrained ones, with a root mean square (rms) deviation of 60 cm − 1 . In the even parity, the four known configurations 5 f 4 7 s , 5 f 4 6 d , 5 f 2 6 d 2 7 s , 5 f 2 6 d 7 s 2 and the unknown 5 f 2 6 d 3 form a basis for interpreting 125 levels with a rms deviation of 84 cm − 1 . Due to perturbations, the theoretical description of the higher configurations 5 f 3 7 s 7 p + 5 f 3 6 d 7 p remains unsatisfactory. The known and predicted levels of U II are used for a determination of the partition function. The parametric study led us to a re-investigation of high resolution ultraviolet spectrum of uranium recorded at the Meudon Observatory in the late eighties, of which the analysis was unachieved. In the course of the present study, a number of 451 lines of U II has been classified in the region 2344 –2955 Å. One new level has been established as 5 f 3 6 d 7 p ( 4 I ) 6 K ( J = 5.5 ) at 39113.98 ± 0.1 cm − 1 .

]]>Atoms doi: 10.3390/atoms5020023

Authors: Swapnil Tauheed Ahmad

The present investigation reports on the extended study of the third spectrum of indium (In III). This spectrum was previously analyzed in many articles, but, nevertheless, this study represents a significant extension of the previous analyses. The main new contribution is connected to the observation of transitions involving core-excited configurations. Previous data are critically evaluated and in some cases are corrected. The spectra were recorded on 3-m as well as on 10.7-m normal incidence spectrographs using a triggered spark source. Theoretical calculations were made with Cowan’s code. The analysis results in the identifications of 70 spectral lines and determination of 24 new energy levels. In addition, the manuscript represents a compilation of all presently available data on In III.

]]>Atoms doi: 10.3390/atoms5020022

Authors: Jean-Christophe Pain Franck Gilleron Maxime Comet

Nowadays, several opacity codes are able to provide data for stellar structure models, but the computed opacities may show significant differences. In this work, we present state-of-the-art precise spectral opacity calculations, illustrated by stellar applications. The essential role of laboratory experiments to check the quality of the computed data is underlined. We review some X-ray and XUV laser and Z-pinch photo-absorption measurements as well as X-ray emission spectroscopy experiments involving hot dense plasmas produced by ultra-high-intensity laser irradiation. The measured spectra are systematically compared with the fine-structure opacity code SCO-RCG. The focus is on iron, due to its crucial role in understanding asteroseismic observations of β Cephei-type and Slowly Pulsating B stars, as well as of the Sun. For instance, in β Cephei-type stars, the iron-group opacity peak excites acoustic modes through the “kappa-mechanism”. Particular attention is paid to the higher-than-predicted iron opacity measured at the Sandia Z-machine at solar interior conditions. We discuss some theoretical aspects such as density effects, photo-ionization, autoionization or the “filling-the-gap” effect of highly excited states.

]]>Atoms doi: 10.3390/atoms5020020

Authors: Luning Liu Deirdre Kilbane Padraig Dunne Xinbing Wang Gerry O’Sullivan

Configuration interaction (CI) effects can greatly influence the way in which extreme ultraviolet (EUV) and soft X-ray (SXR) spectra of heavier ions are dominated by emission from unresolved transition arrays (UTAs), the most intense of which originate from Δn = 0, 4p64dN+1−4p54dN+2+4p64dN4f1 transitions. Changing the principle quantum number n, from 4 to 5, changes the origin of the UTA from Δn = 0, 4p64dN+1−4p54dN+2+4p64dN4f1 to Δn = 0, 5p65dN+1−5p55dN+2+5p65dN5f1 transitions. This causes unexpected and significant changes in the impact of configuration interaction from that observed in the heavily studied n = 4 – n = 4 arrays. In this study, the properties of n = 5 – n = 5 arrays have been investigated theoretically with the aid of Hartree-Fock with configuration interaction (HFCI) calculations. In addition to predicting the wavelengths and spectral details of the anticipated features, the calculations show that the effects of configuration interaction are quite different for the two different families of Δn = 0 transitions, a conclusion which is reinforced by comparison with experimental results.

]]>Atoms doi: 10.3390/atoms5020021

Authors: Chun-Woo Lee

Development in mathematical formulations of parameterizing the resonance structures using the phase-shifted multichannel quantum defect theory (MQDT) and their use in analyzing the effect of inter-series interactions on the autoionizing Rydberg spectra is reviewed. Reformulation of the short-range scattering matrix into the form analogous to S = SBSR in scattering theory are the crucial step in this development. Formulation adopts different directions and goals depending on whether autoionizing series converge to the same limit (degenerate) or to different limits (nondegenerate) because of the different nature of the perturbation. For the nondegenerate case, finding the simplest form of profile index functions of the autoionizing spectra with the minimal number of parameters is the main goal and some results are reviewed. For the degenerate case where perturbation acts uniformly throughout the entire series, isolation of the overlapped autoionizing series into the unperturbed autoionizing series is the key objective in research and some results in that direction are reviewed.

]]>Atoms doi: 10.3390/atoms5020018

Authors: Roberto Celiberto Mario Capitelli Gianpiero Colonna Giuliano D’Ammando Fabrizio Esposito Ratko Janev Vincenzo Laporta Annarita Laricchiuta Lucia Pietanza Maria Rutigliano Jogindra Wadehra

We report cross-sections and rate coefficients for excited states colliding with electrons, heavy particles and walls useful for the description of H 2 /He plasma kinetics under different conditions. In particular, the role of the rotational states in resonant vibrational excitations of the H 2 molecule by electron impact and the calculation of the related cross-sections are illustrated. The theoretical determination of the cross-section for the rovibrational energy exchange and dissociation of H 2 molecule, induced by He atom impact, by using the quasi-classical trajectory method is discussed. Recombination probabilities of H atoms on tungsten and graphite, relevant for the determination of the nascent vibrational distribution, are also presented. An example of a state-to-state plasma kinetic model for the description of shock waves operating in H 2 and He-H 2 mixtures is presented, emphasizing also the role of electronically-excited states in affecting the electron energy distribution function of free electrons. Finally, the thermodynamic properties and the electrical conductivity of non-ideal, high-density hydrogen plasma are finally discussed, in particular focusing on the pressure ionization phenomenon in high-pressure high-temperature plasmas.

]]>Atoms doi: 10.3390/atoms5020019

Authors: Kanti Aggarwal Akinori Igarashi Francis Keenan Shinobu Nakazaki

We report calculations of energy levels, radiative rates, collision strengths and effective collision strengths for transitions among the lowest 25 levels of the n ≤ 5 configurations of He II. The general-purpose relativistic atomic structure package (grasp) and Dirac atomic R-matrix code (darc) are adopted for the calculations. Radiative rates, oscillator strengths and line strengths are reported for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2) and magnetic quadrupole (M2) transitions among the 25 levels. Furthermore, collision strengths and effective collision strengths are listed for all 300 transitions among the above 25 levels over a wide energy (temperature) range up to 9 Ryd (10 5.4 K). Comparisons are made with earlier available results, and the accuracy of the data is assessed.

]]>Atoms doi: 10.3390/atoms5020017

Authors: Anand Bhatia

In a previous paper (Bhatia A.K. 2016), a hybrid theory for the scattering of positrons from hydrogen atoms was applied to calculate S-wave phase shifts, annihilation, and positronium formation cross sections. This approach is now being applied to calculate P-wave positron-hydrogen scattering. The present results, obtained using short-range correlation functions along with long-range correlations in the Schrödinger equation at the same time, agree very well with the results obtained in an earlier calculation by Bhatia et al. (1974), using the Feshbach projection operator formalism. In these earlier calculations, the correction due to the long-range correlations was applied to the variational results. In spite of the fact that this ad hoc correction destroyed the variational bound, the final results have been considered accurate. Annihilation cross-sections, positronium formation cross-sections, calculated in the distorted-wave approximation, are also presented.

]]>Atoms doi: 10.3390/atoms5020016

Authors: Per Jönsson Gediminas Gaigalas Pavel Rynkun Laima Radžiūtė Jörgen Ekman Stefan Gustafsson Henrik Hartman Kai Wang Michel Godefroid Charlotte Froese Fischer Ian Grant Tomas Brage Giulio Del Zanna

Atomic data, such as wavelengths, spectroscopic labels, broadening parameters and transition rates, are necessary for many applications, especially in plasma diagnostics, and for interpreting the spectra of distant astrophysical objects. The experiment with its limited resources is unlikely to ever be able to provide a complete dataset on any atomic system. Instead, the bulk of the data must be calculated. Based on fundamental principles and well-justified approximations, theoretical atomic physics derives and implements algorithms and computational procedures that yield the desired data. We review progress and recent developments in fully-relativistic multiconfiguration Dirac–Hartree–Fock methods and show how large-scale calculations can give transition energies of spectroscopic accuracy, i.e., with an accuracy comparable to the one obtained from observations, as well as transition rates with estimated uncertainties of a few percent for a broad range of ions. Finally, we discuss further developments and challenges.

]]>Atoms doi: 10.3390/atoms5020015

Authors: Jen-Hao Ou Yew Ho

We provide benchmark values for Shannon information entropies in position space for the ground state and ls2s 1Se excited state of helium confined with finite confinement potentials by employing the highly correlated Hylleraas-type wave functions. For the excited state, a “tilt” (small oscillation) on the curve of Shannon entropy as a function of width size for the confinement potential is observed. Justified by the behavior of the electron density, the localization or delocalization of the helium wave functions confined with repulsive and attractive finite oscillator (FO) potentials are examined.

]]>Atoms doi: 10.3390/atoms5010014

Authors: Kyle Leach Iris Dillmann Renee Klawitter Erich Leistenschneider Annika Lennarz Thomas Brunner Dieter Frekers Corina Andreoiu Anna Kwiatkowski Jens Dilling

Several modes of electroweak radioactive decay require an interaction between the nucleus and bound electrons within the constituent atom. Thus, the probabilities of the respective decays are not only influenced by the structure of the initial and final states in the nucleus, but can also depend strongly on the atomic charge. Conditions suitable for the partial or complete ionization of these rare isotopes occur naturally in hot, dense astrophysical environments, but can also be artificially generated in the laboratory to selectively block certain radioactive decay modes. Direct experimental studies on such scenarios are extremely difficult due to the laboratory conditions required to generate and store radioactive ions at high charge states. A new electron-beam ion trap (EBIT) decay setup with the TITAN experiment at TRIUMF has successfully demonstrated such techniques for performing spectroscopy on the radioactive decay of highly charged ions.

]]>Atoms doi: 10.3390/atoms5010013

Authors: Momoe Mita Hiroyuki Sakaue Daiji Kato Izumi Murakami Nobuyuki Nakamura

We present a direct observation of the M1 transition between the fine structure splitting in the 4 f 13 5 s 2 5 p 6 2 F ground term of W VIII. The spectroscopic data of few-times ionized tungsten ions are important for the future ITER diagnostics, but there is a serious lack of data. The present study is part of an ongoing effort to solve this problem. Emission from the tungsten ions produced and trapped in a compact electron beam ion trap is observed with a Czerny–Turner visible spectrometer. Spectra in the EUV range are also observed at the same time to help identify the previously-unreported visible lines. The observed wavelength 574.47 ± 0.03 nm (air), which corresponds to the fine structure splitting of 17,402.5 ± 0.9 cm − 1 , shows reasonable agreement with the previously reported value 17,410 ± 5 cm − 1 obtained indirectly through the analysis of EUV spectra [Ryabtsev et al., Atoms 3 (2015) 273].

]]>Atoms doi: 10.3390/atoms5010012

Authors: Jorge Reyna Almandos Mónica Raineri

This article presents a review concerning the spectral analysis of several ions of neon, argon, krypton and xenon, with impact on laser studies and astrophysics that were mainly carried out in our collaborative groups between Argentina and Brazil during many years. The spectra were recorded from the vacuum ultraviolet to infrared regions using pulsed discharges. Semi-empirical approaches with relativistic Hartree–Fock and Dirac-Fock calculations were also included in these investigations. The spectral analysis produced new classified lines and energy levels. Lifetimes and oscillator strengths were also calculated.

]]>Atoms doi: 10.3390/atoms5010011

Authors: Alexander Ryabtsev Edward Kononov

The spectrum of silver, excited in a vacuum spark, was recorded in the region 150–350 Å on a 3-m grazing incidence spectrograph. The resonance 4dk–(4dk−15p + 4dk−14f + 4p54dk+1) was studied in the Ag6+–Ag8+ spectra (Ag VII–Ag IX) with k = 5–3, respectively. Several hundred lines were identified with the aid of the Cowan code and orthogonal operator technique calculations. The energy levels were found and the transition probabilities were calculated.

]]>Atoms doi: 10.3390/atoms5010010

Authors: Laurentius Windholz

For the determination of improved energy levels of ionic spectra of elements with large values of nuclear magnetic dipole moment (and eventually large values of nuclear quadrupole moments), it is necessary to determine the center of gravity of spectral lines from resolved hyperfine structure patterns appearing in highly resolved spectra. This is demonstrated on spectral lines of Ta II, Pr II and La II. Blend situations (different transitions with accidentally nearly the same wave number difference between the combining levels) must also be considered.

]]>Atoms doi: 10.3390/atoms5010009

Authors: Alexander Kramida Gillian Nave Joseph Reader

New wavelength measurements in the vacuum ultraviolet (VUV), ultraviolet and visible spectral regions have been combined with available literature data to refine and extend the description of the spectrum of singly ionized copper (Cu II). In the VUV region, we measured 401 lines using a concave grating spectrograph and photographic plates. In the UV and visible regions, we measured 276 lines using a Fourier-transform spectrometer. These new measurements were combined with previously unpublished data from the thesis of Ross, with accurate VUV grating measurements of Kaufman and Ward, and with less accurate older measurements of Shenstone to construct a comprehensive list of ≈2440 observed lines, from which we derived a revised set of 379 optimized energy levels, complemented with 89 additional levels obtained using series formulas. Among the 379 experimental levels, 29 are new. Intensities of all lines observed in different experiments have been reduced to the same uniform scale by using newly calculated transition probabilities (A-values). We combined our calculations with published measured and calculated A-values to provide a set of 555 critically evaluated transition probabilities with estimated uncertainties, 162 of which are less than 20%.

]]>Atoms doi: 10.3390/atoms5010008

Authors: Alan Hibbert

Recent experimental work by Belmonte et al. (2014) has given rates for some 4p–4d transitions that are significantly at variance with the previous experimental work of Rudko and Tang (1967) recommended in the NIST tabulations. To date, there are no theoretical rates with which to compare. In this work, we provide such theoretical data. We have undertaken a substantial and systematic configuration interaction calculation, with an extrapolation process applied to ab initio mixing coefficients, which gives energy differences in agreement with experiment. The length and velocity forms give values that are within 10%–15% of each other. Our results are in sufficiently close agreement with those of Belmonte et al. that we can confidently recommend that their results are much more accurate than the early results of Rudko and Tang, and should be adopted in place of the latter.

]]>Atoms doi: 10.3390/atoms5010007

Authors: Charlotte Fischer Gediminas Gaigalas Per Jönsson

Allenergylevelsofthe3dk,k=1,2,...,8,9,conﬁgurationsfortungstenions,computedusing the GRASP2K fully relativistic code based on the variational multiconﬁguration Dirac–Hartree–Fock method, are reported. Included in the calculations are valence correlation where all 3s,3p,3d orbitals are considered to be valence orbitals, as well as core–valence and core–core effects from the 2s,2p subshells. Results are compared with other recent theory and with levels obtained from the wavelengths of lines observed in the experimental spectra. It is shown that the core correlation effects considerably reduce the disagreement with levels linked directly to observed wavelengths, but may differ signiﬁcantly from the NIST levels, where an unknown shift of the levels could not be determined from experimental wavelengths. For low values of k, levels were in good agreement with relativistic many-body perturbation levels, but for 2 &lt; k &lt; 8, the present results were in better agreement with observation.

]]>Atoms doi: 10.3390/atoms5010006

Authors: Gediminas Gaigalas Charlotte Fischer Pavel Rynkun Per Jönsson

The JJ2LSJ program, which is important not only for the GRASP2K package but for the atom theory in general, is presented. The program performs the transformation of atomic state functions(ASFs) from a jj-coupled CSF basis into an LSJ-coupled CSF basis. In addition, the program implements a procedure that assigns a unique label to all energy levels. Examples of how to use the JJ2LSJ program are given. Several cases are presented where there is a unique labeling problem.

]]>Atoms doi: 10.3390/atoms5010004

Authors: Sven Sturm Manuel Vogel Florian Köhler-Langes Wolfgang Quint Klaus Blaum Günter Werth

Highly charged ions represent environments that allow to study precisely one or more bound electrons subjected to unsurpassed electromagnetic fields. Under such conditions, the magnetic moment (g-factor) of a bound electron changes significantly, to a large extent due to contributions from quantum electrodynamics. We present three Penning-trap experiments, which allow to measure magnetic moments with ppb precision and better, serving as stringent tests of corresponding calculations, and also yielding access to fundamental quantities like the fine structure constant α and the atomic mass of the electron. Additionally, the bound electrons can be used as sensitive probes for properties of the ionic nuclei. We summarize the measurements performed so far, discuss their significance, and give a detailed account of the experimental setups, procedures and the foreseen measurements.

]]>Atoms doi: 10.3390/atoms5010005

Authors: Dylan Del Papa Richard Holt S. Rosner

Using fast-ion-beam laser-fluorescence spectroscopy (FIBLAS), we have measured the hyperfine structure (hfs) of 14 levels and an additional four transitions in Dy II and the isotope shifts (IS) of 12 transitions in the wavelength range of 422–460 nm. These are the first precision measurements of this kind in Dy II. Along with hfs and IS, new undocumented transitions were discovered within 3 GHz of the targeted transitions. These atomic data are essential for astrophysical studies of chemical abundances, allowing correction for saturation and the effects of blended lines. Lanthanide abundances are important in diffusion modeling of stellar interiors, and in the mechanisms and history of nucleosynthesis in the universe. Hfs and IS also play an important role in the classification of energy levels, and provide a benchmark for theoretical atomic structure calculations.

]]>Atoms doi: 10.3390/atoms5010003

Authors: Stefan Gustafsson Per Jönsson Charlotte Froese Fischer Ian Grant

Large configuration interaction (CI) calculations can be performed if part of the interaction is treated perturbatively. To evaluate the combined CI and perturbative method, we compute excitation energies for the 3 l 3 l ′ , 3 l 4 l ′ and 3 s 5 l states in Mg-like iron. Starting from a CI calculation including valence and core–valence correlation effects, it is found that the perturbative inclusion of core–core electron correlation halves the mean relative differences between calculated and observed excitation energies. The effect of the core–core electron correlation is largest for the more excited states. The final relative differences between calculated and observed excitation energies is 0.023%, which is small enough for the calculated energies to be of direct use in line identifications in astrophysical and laboratory spectra.

]]>Atoms doi: 10.3390/atoms5010002

Authors: Arijit Ghoshal Yew Ho

The effect of Debye plasma on the 1 s 2 s 2 2 S resonance states in the scattering of electron from helium atom has been investigated within the framework of the stabilization method. The interactions among the charged particles in Debye plasma have been modelled by Debye–Huckel potential. The 1 s 2 s excited state of the helium atom has been treated as consisting of a H e + ionic core plus an electron moving around. The interaction between the core and the electron has then been modelled by a model potential. It has been found that the background plasma environment significantly affects the resonance states. To the best of our knowledge, such an investigation of 1 s 2 s 2 2 S resonance states of the electron–helium system embedded in Debye plasma environment is the first reported in the literature.

]]>Atoms doi: 10.3390/atoms5010001

Authors: Atoms Editorial Office

The editors of Atoms would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2016.[...]

]]>Atoms doi: 10.3390/atoms4040031

Authors: Joseph Reader

The analysis of the spectrum of four-times-ionized yttrium, Y V, was extended to provide a large number of new spectrum lines and energy levels. The new analysis is based on spectrograms made with sliding-spark discharges on 10.7 m normal- and grazing-incidence spectrographs. The measurements cover the region 184–2549 Å. The results revise levels for this spectrum by Zahid-Ali et al. (1975) and by Ateqad et al. (1984). Five hundred and seventy lines were classified as transitions between 23 odd-parity and 90 even-parity levels. The 4s24p5, 4s4p6, 4s24p44d, 5s, 5p, 5d, 6s configurations are now complete. Results for the 4s24p46d and 7s configurations are tentative. Ritz-type wavelengths were determined from the optimized energy levels, with uncertainties as low as ±0.0004 Å. The observed configurations were interpreted with Hartree-Fock calculations and least-squares fits of the energy parameters to the observed levels. Oscillator strengths for all classified lines were calculated with the fitted parameters. The results are compared with values for the level energies, percentage compositions, and transition probabilities from recent ab initio theoretical calculations. The ionization energy was revised to 607,760 ± 300 cm−1 (75.353 ± 0.037 eV).

]]>Atoms doi: 10.3390/atoms4040029

Authors: Keiji Sawada Motoshi Goto

A novel rovibrationally resolved collisional-radiative model of molecular hydrogen that includes 4,133 rovibrational levels for electronic states whose united atom principal quantum number is below six is developed. The rovibrational X 1 Σ g + population distribution in a SlimCS fusion demo detached divertor plasma is investigated by solving the model time dependently with an initial 300 K Boltzmann distribution. The effective reaction rate coefficients of molecular assisted recombination and of other processes in which atomic hydrogen is produced are calculated using the obtained time-dependent population distribution.

]]>Atoms doi: 10.3390/atoms4040030

Authors: Mehdi Ayouz Viatcheslav Kokoouline

Cross sections and thermally-averaged rate coefficients for vibration (de-)excitation of HeH + by an electron impact are computed using a theoretical approach that combines the multi-channel quantum defect theory and the UK R-matrix code. Fitting formulas with a few numerical parameters are derived for the obtained rate coefficients. The interval of applicability of the formulas is from 40 to 10,000 K.

]]>Atoms doi: 10.3390/atoms4040028

Authors: Diego Quiñones Benjamin Varcoe

We describe a new mechanism of decoherence in excited atoms as a result of thermal particles scattering by the atomic nucleus. It is based on the idea that a single scattering will produce a sudden displacement of the nucleus, which will be perceived by the electron in the atom as an instant shift in the electrostatic potential. This will leave the atom’s wave-function partially projected into lower-energy states, which will lead to decoherence of the atomic state. The decoherence is calculated to increase with the excitation of the atom, making observation of the effect easier in Rydberg atoms. We estimate the order of the decoherence for photons and massive particles scattering, analyzing several commonly presented scenarios. Our scheme can be applied to the detection of weakly-interacting particles, like those which may be the constituents of Dark Matter, the interaction of which was calculated to have a more prominent effect that the background radiation.

]]>Atoms doi: 10.3390/atoms4040027

Authors: Anand Bhatia

In previous papers (Bhatia A.K. 2007, 2012) a hybrid theory for the scattering of electrons from a hydrogenic system was developed and applied to calculate scattering phase shifts, Feshbach resonances, and photoabsorption processes. This approach is now being applied to the scattering of positrons from hydrogen atoms. Very accurate phase shifts, using the Feshbach projection operator formalism, were calculated previously (Bhatia A.K. et al. 1971 and Bhatia et al. 1974a). The present results, obtained using shorter expansions in the correlation function, along with long-range correlations in the Schrödinger equation, agree very well with the results obtained earlier. The scattering length is also calculated and the present results are compared with the previous results. Annihilation cross-sections, and positronium formation cross-sections, calculated in the distorted-wave approximation, are also presented.

]]>Atoms doi: 10.3390/atoms4040026

Authors: Dirk Wünderlich Ursel Fantz

Population models are a prerequisite for performing qualitative analysis of population densities measured in plasmas or predicting the dependence of plasma emission on parameter variations. Models for atomic helium and hydrogen as well as molecular hydrogen in low-pressure plasmas are introduced. The cross-sections and transition probabilities used as input in the atomic models are known very accurately, and thus a benchmark of these models against experiments is very successful. For H2, in contrast, significant deviations exist between reaction probabilities taken from different literature sources. The reason for this is the more complex internal structure of molecules compared to atoms. Vibrationally resolved models are applied to demonstrate how these deviations affect the model results. Steps towards a consistent input data set are presented: vibrationally resolved Franck–Condon factors, transition probabilities, and ionization cross-sections have been calculated and are available now. Additionally, ro-vibrational models for selected transitions are applied successfully to low-density, low-temperature plasmas. For further improving the accuracy of population models for H2, however, it is necessary to establish a comprehensive data set for ro-vibrationally resolved excitation cross-sections based on the most recent calculation techniques.

]]>Atoms doi: 10.3390/atoms4030025

Authors: Raisa Trubko Alexander Cronin

Decoherence due to photon scattering in an atom interferometer was studied as a function of laser frequency near an atomic resonance. The resulting decoherence (contrast-loss) spectra will be used to calibrate measurements of tune-out wavelengths that are made with the same apparatus. To support this goal, a theoretical model of decoherence spectroscopy is presented here along with experimental tests of this model.

]]>Atoms doi: 10.3390/atoms4030023

Authors: Atsuo Morinaga Motoyuki Murakami Keisuke Nakamura Hiromitsu Imai

In a Ramsey atom interferometer excited by two electromagnetic fields, if atoms are under a time-varying scalar potential during the interrogation time, the phase of the Ramsey fringes shifts owing to the scalar Aharonov–Bohm effect. The phase shift was precisely examined using a Ramsey atom interferometer with a two-photon Raman transition under the second-order Zeeman potential, and a formula for the phase shift was derived. Using the derived formula, the frequency shift due to the scalar Aharonov–Bohm effect in the frequency standards utilizing the Ramsey atom interferometer was discussed.

]]>Atoms doi: 10.3390/atoms4030024

Authors: Kanti Aggarwal

Electron impact excitation collision strengths are calculated for all transitions among 113 levels of the 2s 2 2p 5 , 2s2p 6 , 2s 2 2p 4 3ℓ, 2s2p 5 3ℓ, and 2p 6 3ℓ configurations of F-like W LXVI. For this purpose, Dirac Atomic R-matrix Code (DARC) has been adopted and results are listed over a wide energy range of 1000 to 6000 Ryd. For comparison purposes, analogous calculations have also been performed with the Flexible Atomic Code (FAC), and the results obtained are comparable with those from DARC.

]]>Atoms doi: 10.3390/atoms4030022

Authors: Arun Goyal Indu Khatri Avnindra Singh Man Mohan Rinku Sharma Narendra Singh

In the present paper, the spectroscopic properties and plasma characteristics of Al-like ions are investigated in an extensive and detailed manner by adopting the GRASP2K package based on fully relativistic Multi-Configuration Dirac–Hartree–Fock (MCDHF) wave-functions in the active space approximation. We have presented energy levels for Al-like ions for Valence-Valence (VV) and Core-Valence (CV) correlations under the scheme of active space. We have also provided radiative data for E1 transitions for Al-like ions and studied the variation of the transition wavelength and transition probability for electric dipole (E1) Extreme Ultraviolet (EUV) transitions with nuclear charge. Our calculated energy levels and transition wavelengths match well with available theoretical and experimental results. The discrepancies of the GRASP2K code results with CIV3 and RMPBT (Relativistic Many Body Perturbation Theory) results are also discussed. The variations of the line intensity ratio, electron density, plasma frequency and plasma skin depth with plasma temperature and nuclear charge are discussed graphically in detail for optically thin plasma in Local Thermodynamic Equilibrium (LTE). We believe that our obtained results may be beneficial for comparisons and in fusion and astrophysical plasma research.

]]>Atoms doi: 10.3390/atoms4030021

Authors: Maxwell Gregoire Nathan Brooks Raisa Trubko Alexander Cronin

We present revised measurements of the static electric dipole polarizabilities of K, Rb, and Cs based on atom interferometer experiments presented in [Phys. Rev. A 2015, 92, 052513] but now re-analyzed with new calibrations for the magnitude and geometry of the applied electric ﬁeld gradient. The resulting polarizability values did not change, but the uncertainties were signiﬁcantly reduced. Then, we interpret several measurements of alkali metal atomic polarizabilities in terms of atomic oscillator strengths fik, Einstein coefﬁcients Aik, state lifetimes τk, transition dipole matrix elements Dik, line strengths Sik, and van der Waals C6 coefﬁcients. Finally, we combine atom interferometer measurements of polarizabilities with independent measurements of lifetimes and C6 values in order to quantify the residual contribution to polarizability due to all atomic transitions other than the principal ns-npJ transitions for alkali metal atoms.

]]>Atoms doi: 10.3390/atoms4030020

Authors: Ned Xoubi

In nuclear experimental, training and teaching laboratories such as a subcritical reactor facility, huge measures of external radiation doses could be caused by neutron and gamma radiation. It becomes imperative to place the health and safety of staff and students in the reactor facility under proper scrutiny. The protection of these individuals against ionization radiation is facilitated by expected dose mapping and shielding calculations. A three-dimensional (3D) Monte Carlo model was developed to calculate the dose rate from neutrons and gamma, using the ANSI/ANS-6.1.1 and the ICRP-74 flux-to-dose conversion factors. Estimation for the dose was conducted across 39 areas located throughout the reactor hall of the facility and its training platform. It was found that the range of the dose rate magnitude is between 7.50 E−01 μSv/h and 1.96 E−04 μSv/h in normal operation mode. During reactor start-up/shut-down mode, it was observed that a large area of the facility can experience exposure to a significant radiation field. This field ranges from 2.99 E+03 μSv/h to 3.12 E+01 μSv/h. There exists no noticeable disparity between results using the ICRP-74 or ANSI/ANS-6.1.1 flux-to-dose rate conversion factors. It was found that the dose rate due to gamma rays is higher than that of neutrons.

]]>Atoms doi: 10.3390/atoms4030019

Authors: Brynle Barrett Adam Carew Hermina Beica Andrejs Vorozcovs Alexander Pouliot A. Kumarakrishnan

Echo atom interferometers have emerged as interesting alternatives to Raman interferometers for the realization of precise measurements of the gravitational acceleration g and the determination of the atomic fine structure through measurements of the atomic recoil frequency ω q . Here we review the development of different configurations of echo interferometers that are best suited to achieve these goals. We describe experiments that utilize near-resonant excitation of laser-cooled rubidium atoms by a sequence of standing wave pulses to measure ω q with a statistical uncertainty of 37 parts per billion (ppb) on a time scale of ∼50 ms and g with a statistical precision of 75 ppb. Related coherent transient techniques that have achieved the most statistically precise measurements of atomic g-factor ratios are also outlined. We discuss the reduction of prominent systematic effects in these experiments using off-resonant excitation by low-cost, high-power lasers.

]]>Atoms doi: 10.3390/atoms4020018

Authors: Eric Imhof James Stickney Matthew Squires

Using a thermal gas, we model the signal of a trapped interferometer. This interferometer uses two short laser pulses, separated by time T, which act as a phase grating for the matter waves. Near time 2 T , there is an echo in the cloud’s density due to the Talbot-Lau effect. Our model uses the Wigner function approach and includes a weak residual harmonic trap. The analysis shows that the residual potential limits the interferometer’s visibility, shifts the echo time of the interferometer, and alters its time dependence. Loss of visibility can be mitigated by optimizing the initial trap frequency just before the interferometer cycle begins.

]]>Atoms doi: 10.3390/atoms4020017

Authors: Daniel Diaz Zoltan Papp Chi-Yu Hu

We re-examine the series of resonances found earlier in atomic three-body systems by solving the Faddeev-Merkuriev integral equations. These resonances are rather broad and line up at each threshold with gradually increasing gaps. This lining up takes place in the same way for all thresholds and is irrespective of the spatial symmetry. We relate these resonances to the Gailitis mechanism, which is a consequence of the polarization potential.

]]>