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Atoms, Volume 9, Issue 3 (September 2021) – 35 articles

Cover Story (view full-size image): Tungsten (W) is used as plasma-facing wall material of magnetically confined plasma devices for nuclear fusion energy developments. Emission lines from highly charged tungsten ions in plasmas are, therefore, useful for passive fusion plasma diagnostics. Optical emission lines have a particular usefulness because mirrors and optical fibers are available to prevent detectors from being directly irradiated with 14 MeV neutrons from fusion plasmas. Using an electron-beam-ion trap (EBIT), a versatile apparatus for spectroscopy of highly charged ions, emission lines of W20+–W29+ are newly identified in a near-UV range. Among them, a magnetic-dipole line of W29+ is studied in detail using a collisional–radiative model and a MCDHF method. View this paper.
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Article
Simultaneous Observation of Tungsten Spectra of W0 to W46+ Ions in Visible, VUV and EUV Wavelength Ranges in the Large Helical Device
Atoms 2021, 9(3), 69; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030069 - 17 Sep 2021
Viewed by 625
Abstract
Spectroscopic studies for emissions released from tungsten ions have been conducted in the Large Helical Device (LHD) for contribution to the tungsten transport study in tungsten divertor fusion devices and for expansion of the experimental database of tungsten line emissions. Tungsten ions are [...] Read more.
Spectroscopic studies for emissions released from tungsten ions have been conducted in the Large Helical Device (LHD) for contribution to the tungsten transport study in tungsten divertor fusion devices and for expansion of the experimental database of tungsten line emissions. Tungsten ions are distributed in the LHD plasma by injecting a pellet consisting of a small piece of tungsten metal wire enclosed by a carbon tube. Line emissions from W0, W5+, W6+, W24+–W28+, W37+, W38+, and W41+–W46+ are observed simultaneously in the visible (3200–3550 Å), vacuum ultraviolet (250–1050 Å), and extreme ultraviolet (5–300 Å) wavelength ranges and the wavelengths are summarized. Temporal evolutions of line emissions from these charge states are compared for comprehensive understanding of tungsten impurity behavior in a single discharge. The charge distribution of tungsten ions strongly depends on the electron temperature. Measurements of emissions from W10+ to W20+ are still insufficient, which is addressed as a future task. Full article
(This article belongs to the Special Issue Atomic and Molecular Spectra in Magnetically Confined Torus Plasmas)
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Article
Three-Photon Ionization with One-Photon Resonance between Excited Levels
Atoms 2021, 9(3), 68; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030068 - 17 Sep 2021
Viewed by 373
Abstract
Within the framework of a three-level model, the process of three-photon ionization with one-photon resonance between two excited levels (with the lower one being initially unpopulated) is considered using the density matrix method. It is shown that such resonance can result in the [...] Read more.
Within the framework of a three-level model, the process of three-photon ionization with one-photon resonance between two excited levels (with the lower one being initially unpopulated) is considered using the density matrix method. It is shown that such resonance can result in the appearance of a maximum in the three-photon ionization spectrum when detuning between the resonance wavenumber and the wavenumber of the transition responsible for the lower excited level being populated exceeds the laser radiation linewidth by more than three orders of magnitude. Full article
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Article
Simultaneous Excitation of Helium by Means of an Electron and a Photon: A Joined Experimental and Theoretical Study
Atoms 2021, 9(3), 67; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030067 - 17 Sep 2021
Viewed by 353
Abstract
We report on a joined experimental and theoretical study of differential cross-sections resulting from inelastic scattering of a monoenergetic electron by helium atoms in the presence of an intense carbon dioxide laser. In particular, we measured the signals of the scattered electrons during [...] Read more.
We report on a joined experimental and theoretical study of differential cross-sections resulting from inelastic scattering of a monoenergetic electron by helium atoms in the presence of an intense carbon dioxide laser. In particular, we measured the signals of the scattered electrons during the simultaneous electron–photon excitation of He 21P state for the first three microseconds of the laser pulse. The signals were measured for an incident electron energy of 45 eV and showed a structure that emerged at small scattering angles. The latter was found to be sensitive to the nature of the transferred photons, as well as the intensity of the laser field. The experimental findings were supported by quantum calculations based on the second-order Born approximation in which the correlated electron–electron interactions were taken into account. Full article
(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)
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Article
Revealing the Target Electronic Structure with Under-Threshold RABBITT
Atoms 2021, 9(3), 66; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030066 - 13 Sep 2021
Viewed by 435
Abstract
The process of reconstruction of attosecond beating by interference of two-photon transitions (RABBITT) reveals the target atom electronic structure when one of the transitions proceeds from below the ionization threshold. Such an under-threshold RABBITT resonates with the target bound states and thus maps [...] Read more.
The process of reconstruction of attosecond beating by interference of two-photon transitions (RABBITT) reveals the target atom electronic structure when one of the transitions proceeds from below the ionization threshold. Such an under-threshold RABBITT resonates with the target bound states and thus maps faithfully the discrete energy levels and the corresponding oscillator strengths. We demonstrate this sensitivity by considering the Ne atom driven by the combination of the XUV and IR pulses at the fundmanetal laser frequency in the 800 and 1000 nm ranges. Full article
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Article
In Silico Studies on Selected Neutral Molecules, CGa2Ge2, CAlGaGe2, and CSiGa2Ge Containing Planar Tetracoordinate Carbon
Atoms 2021, 9(3), 65; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030065 - 10 Sep 2021
Viewed by 518
Abstract
Density functional theory (DFT) was used to study the structure, stability, and bonding in some selected neutral pentaatomic systems, viz., CGa2Ge2, CAlGaGe2, and CSiGa2Ge containing planar tetracoordinate carbon. The systems are kinetically stable, as [...] Read more.
Density functional theory (DFT) was used to study the structure, stability, and bonding in some selected neutral pentaatomic systems, viz., CGa2Ge2, CAlGaGe2, and CSiGa2Ge containing planar tetracoordinate carbon. The systems are kinetically stable, as predicted from the ab initio molecular dynamics simulations. The natural bond orbital (NBO) analysis showed that strong electron donation occurs to the central planar carbon atom by the peripheral atoms in all the studied systems. From the nucleus independent chemical shift (NICS) analysis, it is shown that the systems possess both σ- and π- aromaticity. The presence of 18 valence electrons in these systems, in their neutral form, appears to be important for their stability with planar geometries rather than tetrahedral structures. The nature of bonding is understood through the adaptive natural density partitioning analysis (AdNDP), quantum theory of atoms in molecules (QTAIM) analysis, and also via Wiberg bond index (WBI) and electron localization function (ELF). Full article
(This article belongs to the Special Issue Planar Tetracoordinate Carbon—Fifty Years and Beyond)
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Article
Vibrational Excitation Cross-Section by Positron Impact: A Wave-Packet Dynamics Study
Atoms 2021, 9(3), 64; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030064 - 09 Sep 2021
Viewed by 375
Abstract
The vibrational excitation cross-section of a diatomic molecule by positron impact is obtained using wave-packet propagation techniques. The dynamics study was carried on a two-dimensional potential energy surface, which couples a hydrogenlike harmonic oscillator to a positron via a spherically symmetric correlation polarization [...] Read more.
The vibrational excitation cross-section of a diatomic molecule by positron impact is obtained using wave-packet propagation techniques. The dynamics study was carried on a two-dimensional potential energy surface, which couples a hydrogenlike harmonic oscillator to a positron via a spherically symmetric correlation polarization potential. The cross-section for the excitation of the first vibrational mode is in good agreement with previous reports. Our model suggests that a positron couples to the target vibration by responding instantly to an interaction potential, which depends on the target vibrational coordinate. Full article
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Article
Emission Lines in 290–360 nm of Highly Charged Tungsten Ions W20+–W29+
Atoms 2021, 9(3), 63; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030063 - 08 Sep 2021
Viewed by 614
Abstract
Forbidden transitions in the near-UV and visible wavelength of highly charged tungsten (W) ions are potentially useful as novel tungsten diagnostics means of fusion plasmas. Emission lines in 290–360 nm from Wq+ ions interacting with an electron beam of 540–1370 eV [...] Read more.
Forbidden transitions in the near-UV and visible wavelength of highly charged tungsten (W) ions are potentially useful as novel tungsten diagnostics means of fusion plasmas. Emission lines in 290–360 nm from Wq+ ions interacting with an electron beam of 540–1370 eV are measured, using a compact electron-beam-ion-trap. The charge states of 64 lines are identified as W20+–W29+. A magnetic-dipole (M1) line of W29+ between the excited states (4d84f)[(4d5/22)44f7/2]13/2[(4d5/22)44f5/2]13/2 is newly identified; the wavelength is determined as 351.03(10) nm in air. The theoretical wavelength calculated using the multiconfiguration Dirac–Hartree–Fock method is in a good agreement with the measurement. Full article
(This article belongs to the Special Issue Atomic and Molecular Spectra in Magnetically Confined Torus Plasmas)
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Article
Cross Sections and Rate Coefficients for Vibrational Excitation of H2O by Electron Impact
Atoms 2021, 9(3), 62; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030062 - 06 Sep 2021
Viewed by 569
Abstract
Cross-sections and thermally averaged rate coefficients for vibration (de-)excitation of a water molecule by electron impact are computed; one and two quanta excitations are considered for all three normal modes. The calculations use a theoretical approach that combines the normal mode approximation for [...] Read more.
Cross-sections and thermally averaged rate coefficients for vibration (de-)excitation of a water molecule by electron impact are computed; one and two quanta excitations are considered for all three normal modes. The calculations use a theoretical approach that combines the normal mode approximation for vibrational states of water, a vibrational frame transformation employed to evaluate the scattering matrix for vibrational transitions and the UK molecular R-matrix code. The interval of applicability of the rate coefficients is from 10 to 10,000 K. A comprehensive set of calculations is performed to assess uncertainty of the obtained data. The results should help in modelling non-LTE spectra of water in various astrophysical environments. Full article
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Article
Benchmark Angle-Differential Cross-Section Ratios for Excitation of the 4p5s Configuration in Krypton
Atoms 2021, 9(3), 61; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030061 - 02 Sep 2021
Viewed by 455
Abstract
Benchmark intensity ratio measurements of the energy loss lines of krypton for excitation of the 4p61S04p55s[3/2]2, [...] Read more.
Benchmark intensity ratio measurements of the energy loss lines of krypton for excitation of the 4p61S04p55s[3/2]2, 4p55s[3/2]1, 4p55s[1/2]0, and 4p55s[1/2]1 transitions are reported, these being the lowest electronic excitations for krypton. The importance of these ratios as stringent tests of theoretical electron scattering models for the noble gases is discussed, as well as the role of spin-exchange and direct processes regarding the angular dependence of these ratios. The experimental data are compared with predictions from fully-relativistic B-spline R-matrix (close-coupling) calculations. Full article
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Article
Evaluation of Fe XIV Intensity Ratio for Electron Density Diagnostics by Laboratory Measurements
Atoms 2021, 9(3), 60; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030060 - 30 Aug 2021
Viewed by 728
Abstract
The intensity ratio of Fe XIV 264.765A/274.203A is useful to determine the electron density of solar corona, and the relationship between the electron density and the intensity ratio obtained from a model should be evaluated using laboratory plasmas to estimate the electron density [...] Read more.
The intensity ratio of Fe XIV 264.765A/274.203A is useful to determine the electron density of solar corona, and the relationship between the electron density and the intensity ratio obtained from a model should be evaluated using laboratory plasmas to estimate the electron density more precisely. We constructed a new collisional–radiative model (CR-model) for Fe XIV (an Al-like iron ion) by considering the processes of proton-impact excitation and electron-impact ionization to the excited states of a Mg-like iron ion. The atomic data used in the CR-model were calculated using the HULLAC atomic code. The model was evaluated based on laboratory experiments using a compact electron beam ion trap, called CoBIT, and the Large Helical Device (LHD). The measured Fe XIV 264.785 Å/274.203 Å line intensity ratio with CoBIT was 1.869 ± 0.036, and it agreed well with our CR-model results. Concurrently, the measured ratio using LHD was larger than the results of our CR-model and CHIANTI. The estimated electron densities using our CR-model agreed with those from CHIANTI within a factor of 1.6–2.4 in the range of ne101011cm3. Further model development is needed to explain the ratio in a high-electron density region. Full article
(This article belongs to the Special Issue Atomic and Molecular Spectra in Magnetically Confined Torus Plasmas)
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Article
Relativistic Study on the Scattering of e± from Atoms and Ions of the Rn Isonuclear Series
Atoms 2021, 9(3), 59; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030059 - 27 Aug 2021
Viewed by 442
Abstract
Calculations are presented for differential, integrated elastic, momentum transfer, viscosity, inelastic, total cross sections and spin polarization parameters S, T and U for electrons and positrons scattering from atoms and ions of radon isonuclear series in the energy range from 1 eV–1 MeV. [...] Read more.
Calculations are presented for differential, integrated elastic, momentum transfer, viscosity, inelastic, total cross sections and spin polarization parameters S, T and U for electrons and positrons scattering from atoms and ions of radon isonuclear series in the energy range from 1 eV–1 MeV. In addition, we analyze systematically the details of the critical minima in the elastic differential cross sections along with the positions of the corresponding maximum polarization points in the Sherman function for the aforesaid scattering systems. Coulomb glory is investigated across the ionic series. A short range complex optical potential, comprising static, polarization and exchange (for electron projectile) potentials, is used to describe the scattering from neutral atom. This potential is supplemented by the Coulomb potential for the same purpose for a charged atom. The Dirac partial wave analysis, employing the aforesaid potential, is carried out to calculate the aforesaid scattering observables. A comparison of our results with other theoretical findings shows a reasonable agreement over the studied energy range. Full article
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Article
Interferometry in an Atomic Fountain with Ytterbium Bose–Einstein Condensates
Atoms 2021, 9(3), 58; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030058 - 25 Aug 2021
Cited by 1 | Viewed by 403
Abstract
We present enabling experimental tools and atom interferometer implementations in a vertical “fountain” geometry with ytterbium Bose–Einstein condensates. To meet the unique challenge of the heavy, non-magnetic atom, we apply a shaped optical potential to balance against gravity following evaporative cooling and demonstrate [...] Read more.
We present enabling experimental tools and atom interferometer implementations in a vertical “fountain” geometry with ytterbium Bose–Einstein condensates. To meet the unique challenge of the heavy, non-magnetic atom, we apply a shaped optical potential to balance against gravity following evaporative cooling and demonstrate a double Mach–Zehnder interferometer suitable for applications such as gravity gradient measurements. Furthermore, we also investigate the use of a pulsed optical potential to act as a matter wave lens in the vertical direction during expansion of the Bose–Einstein condensate. This method is shown to be even more effective than the aforementioned shaped optical potential. The application of this method results in a reduction of velocity spread (or equivalently an increase in source brightness) of more than a factor of five, which we demonstrate using a two-pulse momentum-space Ramsey interferometer. The vertical geometry implementation of our diffraction beams ensures that the atomic center of mass maintains overlap with the pulsed atom optical elements, thus allowing extension of atom interferometer times beyond what is possible in a horizontal geometry. Our results thus provide useful tools for enhancing the precision of atom interferometry with ultracold ytterbium atoms. Full article
(This article belongs to the Special Issue Atomic Interferometry with Bose–Einstein Condensates)
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Article
Constrained Molecular Dynamic Simulation of the Potential Mean Force of Lithium Bromide Ion Pairs in Acetonitrile
Atoms 2021, 9(3), 57; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030057 - 17 Aug 2021
Viewed by 498
Abstract
Molecular dynamic simulations of Li+, and Br ions in acetonitrile were carried out. The simulated structural properties were compared to experimental data. The solvent potentials of Li+-Br, Li+-Li+, and Br-Br [...] Read more.
Molecular dynamic simulations of Li+, and Br ions in acetonitrile were carried out. The simulated structural properties were compared to experimental data. The solvent potentials of Li+-Br, Li+-Li+, and Br-Br were evaluated using constrained molecular dynamics (CMD) simulations, to determine the solvent contribution to the total force acting on the solute and estimate the liquid arrangements according to the potential of mean force (PMF) values. The PMF of friction kernels and the passage across the Li+-Br barrier was studied using the Grote–Hynes theory. The union-separation development happens in the polarization confining system. Full article
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Article
Deep Minimum and a Vortex for Positronium Formation in Low-Energy Positron-Helium Collisions
Atoms 2021, 9(3), 56; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030056 - 06 Aug 2021
Viewed by 532
Abstract
We find a zero in the positronium formation scattering amplitude and a deep minimum in the logarithm of the corresponding differential cross section for positron–helium collisions for an energy just above the positronium formation threshold. Corresponding to the zero, there is a vortex [...] Read more.
We find a zero in the positronium formation scattering amplitude and a deep minimum in the logarithm of the corresponding differential cross section for positron–helium collisions for an energy just above the positronium formation threshold. Corresponding to the zero, there is a vortex in the extended velocity field that is associated with this amplitude when one treats both the magnitude of the momentum of the incident positron and the angle of the scattered positronium as independent variables. Using the complex Kohn variational method, we determine accurately two-channel K-matrices for positron–helium collisions in the Ore gap. We fit these K-matrices using both polynomials and the Watanabe and Greene’s multichannel effective range theory taking into account explicitly the polarization potential in the Ps-He+ channel. Using the fitted K-matrices we determine the extended velocity field and show that it rotates anticlockwise around the zero in the positronium formation scattering amplitude. We find that there is a valley in the logarithm of the positronium formation differential cross section that includes the deep minimum and also a minimum in the forward direction. Full article
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Article
Redistribution of the Rydberg State Population Induced by Continuous-Spectrum Radiation
Atoms 2021, 9(3), 55; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030055 - 06 Aug 2021
Viewed by 478
Abstract
We consider the redistribution of the Rydberg state population resulting from multistep cascade transitions induced by radiation with a continuous spectrum. The population distribution is analyzed within the space of quantum numbers n and l. The dynamics of the system are studied [...] Read more.
We consider the redistribution of the Rydberg state population resulting from multistep cascade transitions induced by radiation with a continuous spectrum. The population distribution is analyzed within the space of quantum numbers n and l. The dynamics of the system are studied using both the numerical solution of kinetic equations and the diffusion approximation based on the Fokker–Planck equation. The main path of the redistribution process is determined. Full article
(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)
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Article
Microwave Atom Chip Design
Atoms 2021, 9(3), 54; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030054 - 05 Aug 2021
Viewed by 462
Abstract
We present a toolbox of microstrip building blocks for microwave atom chips geared towards trapped atom interferometry. Transverse trapping potentials based on the AC Zeeman (ACZ) effect can be formed from the combined microwave magnetic near fields of a pair or a triplet [...] Read more.
We present a toolbox of microstrip building blocks for microwave atom chips geared towards trapped atom interferometry. Transverse trapping potentials based on the AC Zeeman (ACZ) effect can be formed from the combined microwave magnetic near fields of a pair or a triplet of parallel microstrip transmission lines. Axial confinement can be provided by a microwave lattice (standing wave) along the microstrip traces. Microwave fields provide additional parameters for dynamically adjusting ACZ potentials: detuning of the applied frequency to select atomic transitions and local polarization controlled by the relative phase in multiple microwave currents. Multiple ACZ traps and potentials, operating at different frequencies, can be targeted to different spin states simultaneously, thus enabling spin-specific manipulation of atoms and spin-dependent trapped atom interferometry. Full article
(This article belongs to the Special Issue Atomic Interferometry with Bose–Einstein Condensates)
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Obituary
A Tribute to Oleg Zatsarinny (1953–2021): His Life in Science
Atoms 2021, 9(3), 53; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030053 - 05 Aug 2021
Viewed by 851
Abstract
Oleg Ivanovich Zatsarinny (Figure 1) was born in the city of Uzhgorod, Ukraine, on 4 November 1953 [...] Full article
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Article
Accurate Electron Drift Mobility Measurements in Moderately Dense Helium Gas at Several Temperatures
Atoms 2021, 9(3), 52; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030052 - 04 Aug 2021
Cited by 1 | Viewed by 474
Abstract
We report new accurate measurements of the drift mobility μ of quasifree electrons in moderately dense helium gas in the temperature range 26KT300K for densities lower than those at which states of electrons localized in bubbles appear. [...] Read more.
We report new accurate measurements of the drift mobility μ of quasifree electrons in moderately dense helium gas in the temperature range 26KT300K for densities lower than those at which states of electrons localized in bubbles appear. By heuristically including multiple-scattering effects into classical kinetic formulas, as previously done for neon and argon, an excellent description of the field E, density N, and temperature T dependence of μ is obtained. Moreover, the experimental evidence suggests that the strong decrease of the zero-field density-normalized mobility μ0N with increasing N from the low up to intermediate density regime is mainly due to weak localization of electrons caused by the intrinsic disorder of the system, whereas the further decrease of μ0N for even larger N is due to electron self-trapping in cavities. We suggest that a distinction between weakly localized and electron bubble states can be done by inspecting the behavior of μ0N as a function of N at intermediate densities. Full article
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Article
High Sensitivity Multi-Axes Rotation Sensing Using Large Momentum Transfer Point Source Atom Interferometry
Atoms 2021, 9(3), 51; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030051 - 03 Aug 2021
Viewed by 471
Abstract
A point source interferometer (PSI) is a device where atoms are split and recombined by applying a temporal sequence of Raman pulses during the expansion of a cloud of cold atoms behaving approximately as a point source. The PSI can work as a [...] Read more.
A point source interferometer (PSI) is a device where atoms are split and recombined by applying a temporal sequence of Raman pulses during the expansion of a cloud of cold atoms behaving approximately as a point source. The PSI can work as a sensitive multi-axes gyroscope that can automatically filter out the signal from accelerations. The phase shift arising from the rotations is proportional to the momentum transferred to each atom from the Raman pulses. Therefore, by increasing the momentum transfer, it should be possible to enhance the sensitivity of the PSI. Here, we investigate the degree of enhancement in sensitivity that could be achieved by augmenting the PSI with large momentum transfer (LMT) employing a sequence of many Raman pulses with alternating directions. We analyze how factors such as Doppler detuning, spontaneous emission, and the finite initial size of the atomic cloud compromise the advantage of LMT and how to find the optimal momentum transfer under these limitations, with both the semi-classical model and a model under which the motion of the center of mass of each atom is described quantum mechanically. We identify a set of realistic parameters for which LMT can improve the PSI by a factor of nearly 40. Full article
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Article
Towards B-Spline Atomic Structure Calculations
Atoms 2021, 9(3), 50; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030050 - 31 Jul 2021
Viewed by 590
Abstract
The paper reviews the history of B-spline methods for atomic structure calculations for bound states. It highlights various aspects of the variational method, particularly with regard to the orthogonality requirements, the iterative self-consistent method, the eigenvalue problem, and the related sphf, dbsr-hf, [...] Read more.
The paper reviews the history of B-spline methods for atomic structure calculations for bound states. It highlights various aspects of the variational method, particularly with regard to the orthogonality requirements, the iterative self-consistent method, the eigenvalue problem, and the related sphf, dbsr-hf, and spmchf programs. B-splines facilitate the mapping of solutions from one grid to another. The following paper describes a two-stage approach where the goal of the first stage is to determine parameters of the problem, such as the range and approximate values of the orbitals, after which the level of accuracy is raised. Once convergence has been achieved the Virial Theorem, which is evaluated as a check for accuracy. For exact solutions, the V/T ratio for a non-relativistic calculation is −2. Full article
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Obituary
Scientific Activities of Oleg Zatsarinny in the Ukraine
Atoms 2021, 9(3), 49; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030049 - 26 Jul 2021
Viewed by 525
Abstract
These memoirs about Oleg Ivanovich Zatsarinny (1953–2021) concentrate on his scientific activities in the Ukraine. Full article
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Article
New Transition and Energy Levels of Three-Times Ionized Krypton (Kr IV)
Atoms 2021, 9(3), 48; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030048 - 23 Jul 2021
Viewed by 511
Abstract
A capillary pulsed-discharge and a theta-pinch were used to record Kr spectra in the region of 330–4800 Å. A set of 168 transitions of these spectra were classified for the first time. We extended the analysis to twenty-five new energy levels belonging to [...] Read more.
A capillary pulsed-discharge and a theta-pinch were used to record Kr spectra in the region of 330–4800 Å. A set of 168 transitions of these spectra were classified for the first time. We extended the analysis to twenty-five new energy levels belonging to 3s23p24d, 3s23p25d even configurations. We calculated weighted transition probabilities (gA) for all of the experimentally observed lines and lifetimes for new energy levels using a relativistic Hartree–Fock method, including core-polarization effects. Full article
(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)
Article
Relativistic B-Spline R-Matrix Calculations for Electron Collisions with Ytterbium
Atoms 2021, 9(3), 47; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030047 - 23 Jul 2021
Viewed by 572
Abstract
We have applied the full-relativistic Dirac B-Spline R-matrix method to obtain cross sections for electron scattering from ytterbium atoms. The results are compared with those obtained from a semi-relativistic (Breit-Pauli) model-potential approach and the few available experimental data. Full article
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Article
Spectra of Ga-Like to Cu-Like Praseodymium and Neodymium Ions Observed in the Large Helical Device
Atoms 2021, 9(3), 46; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030046 - 14 Jul 2021
Viewed by 590
Abstract
Extreme ultraviolet (EUV) spectra of highly charged praseodymium (Pr) and neodymium (Nd) ions have been investigated in optically thin high-temperature plasmas produced in the Large Helical Device (LHD), a magnetically confined torus device for fusion research. Discrete spectral lines emitted mainly from highly [...] Read more.
Extreme ultraviolet (EUV) spectra of highly charged praseodymium (Pr) and neodymium (Nd) ions have been investigated in optically thin high-temperature plasmas produced in the Large Helical Device (LHD), a magnetically confined torus device for fusion research. Discrete spectral lines emitted mainly from highly charged ions having 4s or 4p outermost electrons were observed in plasmas with electron temperatures of 0.8–1.8 keV. Most of the isolated lines of Ga-like to Cu-like Nd ions were identified by a comparison with the recent data recorded in an electron beam ion trap (EBIT). The isolated lines of Pr ions corresponding to the identified lines of Nd ions were easily assigned from a similarity of the spectral feature for these two elements. As a result, some of the lines of Pr ions have been newly identified experimentally for the first time in this study. Full article
(This article belongs to the Special Issue Atomic and Molecular Spectra in Magnetically Confined Torus Plasmas)
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Article
EUV Beam-Foil Spectra of Titanium, Iron, Nickel, and Copper
Atoms 2021, 9(3), 45; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030045 - 13 Jul 2021
Viewed by 586
Abstract
Beam–foil spectroscopy offers the efficient excitation of the spectra of a single element as well as time-resolved observation. Extreme-ultraviolet (EUV) beam–foil survey and detail spectra of Ti, Fe, Ni, and Cu are presented, as well as survey spectra of Fe and Ni obtained [...] Read more.
Beam–foil spectroscopy offers the efficient excitation of the spectra of a single element as well as time-resolved observation. Extreme-ultraviolet (EUV) beam–foil survey and detail spectra of Ti, Fe, Ni, and Cu are presented, as well as survey spectra of Fe and Ni obtained at an electron beam ion trap. Various details are discussed in the context of line intensity ratios, yrast transitions, prompt and delayed spectra, and intercombination transitions. Full article
(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)
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Article
One-Electron Energy Spectra of Heavy Highly Charged Quasimolecules: Finite-Basis-Set Approach
Atoms 2021, 9(3), 44; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030044 - 13 Jul 2021
Cited by 1 | Viewed by 557
Abstract
The generalized dual-kinetic-balance approach for axially symmetric systems is employed to solve the two-center Dirac problem. The spectra of one-electron homonuclear quasimolecules are calculated and compared with the previous calculations. The analysis of the monopole approximation with two different choices of the origin [...] Read more.
The generalized dual-kinetic-balance approach for axially symmetric systems is employed to solve the two-center Dirac problem. The spectra of one-electron homonuclear quasimolecules are calculated and compared with the previous calculations. The analysis of the monopole approximation with two different choices of the origin is performed. Special attention is paid to the lead and xenon dimers, Pb82+–Pb82+–e and Xe54+–Xe54+–e, where the energies of the ground and several excited σ-states are presented in the wide range of internuclear distances. The developed method provides the quasicomplete finite basis set and allows for the construction of perturbation theory, including within the bound-state QED. Full article
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Article
On the Electron Impact Integral Cross-Sections for Butanol and Pentanol Isomers
Atoms 2021, 9(3), 43; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030043 - 13 Jul 2021
Viewed by 651
Abstract
The need for a reliable and comprehensive database of cross-sections for many atomic and molecular species is immense due to its key role in R&D domains such as plasma modelling, bio-chemical processes, medicine and many other natural and technological environments. Elastic, momentum transfer [...] Read more.
The need for a reliable and comprehensive database of cross-sections for many atomic and molecular species is immense due to its key role in R&D domains such as plasma modelling, bio-chemical processes, medicine and many other natural and technological environments. Elastic, momentum transfer and total cross-sections of butanol and pentanol isomers by the impact of 6–5000 eV electrons are presented in this work. The calculations were performed by employing the spherical complex optical potential formalism along with single-centre expansion and group additivity rule. The investigations into the presence of isomeric variations reveal that they are more pronounced at low and intermediate energies. Elastic, total cross-sections (with the exception of n-pentanol) and momentum transfer cross-sections for all pentanol isomers are reported here for the first time, to the best of our knowledge. Our momentum transfer cross-sections for butanol isomers are in very good agreement with the experimental and theoretical values available, and in reasonable consensus for other cross-sections. Full article
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Article
A Fully Relativistic Approach to Photon Scattering and Photoionization of Alkali Atoms
Atoms 2021, 9(3), 42; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030042 - 08 Jul 2021
Viewed by 674
Abstract
A fully relativistic approach to calculating photoionization and photon-atom scattering cross sections for quasi one-electron atoms is presented. An extensive set of photoionization cross sections have been calculated for alkali atoms: lithium, sodium, potassium, rubidium and cesium. The importance of relativistic effects and [...] Read more.
A fully relativistic approach to calculating photoionization and photon-atom scattering cross sections for quasi one-electron atoms is presented. An extensive set of photoionization cross sections have been calculated for alkali atoms: lithium, sodium, potassium, rubidium and cesium. The importance of relativistic effects and core polarization on the depth and position of the Cooper minimum in the photoionization cross section is investigated. Good agreement was found with previous Dirac-based B-spline R-matrix calculations of Zatsarinny and Tayal and recent experimental results. Full article
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Communication
Classical Description of Resonant Charge Exchange Involving the Second Flavor of Hydrogen Atoms
Atoms 2021, 9(3), 41; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030041 - 07 Jul 2021
Viewed by 692
Abstract
We studied the consequences of the existence of the second flavor of hydrogen atoms (SFHA)—the existence proven by atomic experiments and evidenced by astrophysical observations—on the resonant charge exchange. We found analytically that there is indeed an important difference in the corresponding cross-sections [...] Read more.
We studied the consequences of the existence of the second flavor of hydrogen atoms (SFHA)—the existence proven by atomic experiments and evidenced by astrophysical observations—on the resonant charge exchange. We found analytically that there is indeed an important difference in the corresponding cross-sections for the SFHA compared to the usual hydrogen atoms. This difference could serve as an additional tool for distinguishing between the two kinds of hydrogen atoms in future experiments/observations. We also show that the SFHA does not exhibit any Stark effect—whether in a uniform or a non-uniform electric field—in any order of the perturbation theory. Full article
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Tutorial
Classical and Quantum Collective Recoil Lasing: A Tutorial
Atoms 2021, 9(3), 40; https://0-doi-org.brum.beds.ac.uk/10.3390/atoms9030040 - 06 Jul 2021
Viewed by 541
Abstract
Collective atomic recoil lasing (CARL) is a process during which an ensemble of cold atoms, driven by a far-detuned laser beam, spontaneously organize themselves in periodic structures on the scale of the optical wavelength. The principle was envisaged by R. Bonifacio in 1994 [...] Read more.
Collective atomic recoil lasing (CARL) is a process during which an ensemble of cold atoms, driven by a far-detuned laser beam, spontaneously organize themselves in periodic structures on the scale of the optical wavelength. The principle was envisaged by R. Bonifacio in 1994 and, ten years later, observed in a series of experiments in Tübingen by C. Zimmermann and colleagues. Here, we review the basic model of CARL in the classical and in the quantum regime. Full article
(This article belongs to the Special Issue Collective Atomic and Free-Electron Lasing)
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