Atoms doi: 10.3390/atoms7030091

Authors: Masahiko Emoto Izumi Murakami Daiji Kato Masanobu Yoshida Masatoshi Kato Setsuo Imazu

The NIFS (National Institute for Fusion Science) Atom and Molecular Database, which has been available online since 1997, is a numerical atomic and molecular database of collision processes that is important for fusion research. This database provides the following: (1) the cross-sections and rate coefficients for ionization, excitation, and recombination caused by electron impact; (2) the charge transfer caused by heavy particle collision and collision processes of molecules; and (3) the sputtering yields of solids and backscattering coefficients from solids. It also offers a bibliographic database. We recently reconstructed the database system. The main purpose of the reconstruction was to migrate the database into an open-source architecture to make the system more flexible and extensible. The previous system used proprietary software and was difficult to customize. The new system consists of open-source software, including PostgreSQL database and Ruby on Rails. New features were also added to the system. The most important improvement is the interface with the Virtual Atomic and Molecular Data Center (VAMDC) portal. Using this interface, researchers can search for data in the NIFS database as well as in various other online databases simultaneously.

]]>Atoms doi: 10.3390/atoms7030090

Authors: Malay Bikas Chowdhuri Joydeep Ghosh Ritu Dey Sharvil Patel Nandini Yadava Ranjana Manchanda Amrita Bhattacharya Izumi Murakami Aditya Team Aditya Team

Oxygen impurity transport in the typical discharges of the Aditya tokamak was investigated using emissivity radial profile of emissivity of the spectral line (2p3p 3D3&ndash;2p3d 3F4) at 650.024 nm from the Be-like oxygen ion. This O4+ spectral line was recorded using a 1.0 m multi-track spectrometer capable of simultaneous measurements from eight lines of sight passing through the plasma. The oxygen transport coefficients were determined by reproducing the experimentally measured emissivity profiles of O4+, using a one-dimensional impurity transport code, STRAHL, and photon emissivity coefficient (PEC) belonging to that transition. The PEC values were obtained from both ADAS and NIFS atomic databases. Using both the databases, much higher values of diffusion coefficients compared to the neo-classical values were observed in both high and low magnetic field edge regions of typical Aditya tokamak Ohmic plasma. Although, almost similar profiles of diffusion coefficients were obtained using PEC values from both databases, the magnitude differs considerably. The maximum values of diffusion coefficients in the plasma edge at low field side of tokamak were ~45 and ~25 m2&middot;s&minus;1 when modeling was done using the ADAS and NIFS databases, respectively. Further analysis on the atomic data used in the calculation indicates that the difference in diffusion coefficients is mainly related to the variation in the values of atomic data of the two databases.

]]>Atoms doi: 10.3390/atoms7030089

Authors: John Shaw David Monismith Yixiao Zhang Danielle Doerr Himadri S. Chakraborty

We compare the electron dynamics at monocrystalline Cu(111), Au(100) and Pd(111) precursor substrates with vicinal nanosteps. The unoccupied bands of a surface superlattice are populated via the resonant charge transfer (RCT) between the surface and a H &minus; ion that flies by at grazing angles. A quantum mechanical wave packet propagation approach is used to simulate the motion of the active electron, and time-evolved wave packet densities are used to visualize the dynamics through the superlattice. The survived ion fraction in the reflected beam generally exhibits modulations as a function of the vicinal terrace size and shows peaks at those energies that access the image state subband dispersions. Differences in magnitudes of the ion-survival as a function of the particular substrate selection and the ion-surface interaction time, based on the choice of two ion-trajectories, are examined. A square well model, producing standing waves between the steps on the surface, explains the energies of the maxima in the ion survival probability for all the metals considered. This indicates that the primary process of confinement induced subband formation is robust. The work may motivate measurements and applications of shallow-angle ion-scattering spectroscopy to access electronic substructures in periodically nanostructured surfaces.

]]>Atoms doi: 10.3390/atoms7030088

Authors: Duško Borka Vesna Borka Jovanović

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

]]>Atoms doi: 10.3390/atoms7030087

Authors: Nandini Yadava Joydeep Ghosh Malay Bikas Chowdhuri Ranjana Manchanda Sripathi Punchithaya K Ritu Dey Kumarpalsinh A. Jadeja Rakesh L. Tanna Deepti Tripathi Aditya-U Team Aditya-U Team

The spatial profile of neutral hydrogen temperatures in Aditya-U tokamak plasma has been estimated from the spatial profile of the H&alpha; spectral emissions measured using a high-resolution multi-track spectrometer, having a spectral resolution of 0.023 nm at a 50 &mu;m entrance slit width. The neutral temperature estimation from the Doppler broadened spectral line was carried out after considering the Zeeman effect due to the magnetic field present in the tokamak. To accurately obtain the temperature of the neutral hydrogen, two temperature components (warm and hot) were required to be considered. A code was developed to obtain the neutral temperature and is used to analyze two typical plasma discharges. The temperature of warm components varies between 3 and 5 eV, while hot atoms have temperatures in the range of 15&ndash;30 eV. It was observed that the chord-integrated neutral temperature increases slightly towards the plasma core region compared to the plasma edge of Aditya-U tokamak.

]]>Atoms doi: 10.3390/atoms7030086

Authors: David M. Surmick Daryl J. Dagel Christian G. Parigger

Spatially resolved, line-of-sight measurements of aluminum monoxide emission spectra in laser ablation plasma are used with Abel inversion techniques to extract radial plasma temperatures. Contour mapping of the radially deconvolved signal intensity shows a ring of AlO formation near the plasma boundary with the ambient atmosphere. Simulations of the molecular spectra were coupled with the line profile fitting routines. Temperature results are presented with simultaneous inferences from lateral, asymmetric radial, and symmetric radial AlO spectral intensity profiles. This analysis indicates that shockwave phenomena in the radial profiles, including a temperature drop behind the blast wave created during plasma initiation were measured.

]]>Atoms doi: 10.3390/atoms7030085

Authors: Reika Kanya Kaoru Yamanouchi

The recent progress in experimental studies of laser-assisted electron scattering (LAES) induced by ultrashort intense laser fields is reviewed. After a brief survey of the theoretical backgrounds of the LAES process and earlier LAES experiments started in the 1970s, new concepts of optical gating and optical streaking for the LAES processes, which can be realized by LAES experiments using ultrashort intense laser pulses, are discussed. A new experimental setup designed for measurements of LAES induced by ultrashort intense laser fields is described. The experimental results of the energy spectra, angular distributions, and laser polarization dependence of the LAES signals are presented with the results of the numerical simulations. A light-dressing effect that appeared in the recorded LAES signals is also shown with the results of the numerical calculations. In addition, as applications of the LAES process, laser-assisted electron diffraction and THz-wave-assisted electron diffraction, both of which have been developed for the determination of instantaneous geometrical structure of molecules, are introduced.

]]>Atoms doi: 10.3390/atoms7030084

Authors: Ashwin P. Rao Matthew T. Cook Howard L. Hall Michael B. Shattan

A hand-held laser-induced breakdown spectroscopy device was used to acquire spectral emission data from laser-induced plasmas created on the surface of cerium-gallium alloy samples with Ga concentrations ranging from 0&ndash;3 weight percent. Ionic and neutral emission lines of the two constituent elements were then extracted and used to generate calibration curves relating the emission line intensity ratios to the gallium concentration of the alloy. The Ga I 287.4-nm emission line was determined to be superior for the purposes of Ga detection and concentration determination. A limit of detection below 0.25% was achieved using a multivariate regression model of the Ga I 287.4-nm line ratio versus two separate Ce II emission lines. This LOD is considered a conservative estimation of the technique&rsquo;s capability given the type of the calibration samples available and the low power (5 mJ per 1-ns pulse) and resolving power ( &lambda; / &Delta; &lambda; = 4000) of this hand-held device. Nonetheless, the utility of the technique is demonstrated via a detailed mapping analysis of the surface Ga distribution of a Ce-Ga sample, which reveals significant heterogeneity resulting from the sample production process.

]]>Atoms doi: 10.3390/atoms7030083

Authors: Eugene Oks

Because of the continuing advances in developing lasers in the far-ultraviolet and x-ray ranges, studies of the behavior of atoms under a high-frequency laser field are of theoretical and practical interest. In the present paper, we review various analytical results obtained by the method of separating rapid and slow subsystems for various polarizations of the laser field. Specifically, we review the corresponding analytical results both in terms of the quantum description of the phenomena involved and in terms of the classical description of the phenomena involved. We point out that, for the classical description of hydrogen atoms in a high-frequency laser field, there are interesting celestial analogies. We discuss hidden symmetries of these physical systems, the advantages of this analytical method, and the connection between these results and the transition to chaos.

]]>Atoms doi: 10.3390/atoms7030082

Authors: Zsolt J. Mezei Michel D. Epée Epée Ousmanou Motapon Ioan F. Schneider

We used the multichannel quantum defect theory to compute cross sections and rate coefficients for the dissociative recombination of CH + initially in its lowest vibrational level v i + = 0 with electrons of incident energy below 0.2 eV. We have focused on the contribution of the 2 2 &Pi; state which is the main dissociative recombination route at low collision energies. The final cross section is obtained by averaging the relevant initial rotational states ( N i + = 0 , ⋯ , 10 ) with a 300 K Boltzmann distribution. The Maxwell isotropic rate coefficients for dissociative recombination are also calculated for different initial rotational states and for electronic temperatures up to a few hundred Kelvins. Our results are compared to storage-ring measurements.

]]>Atoms doi: 10.3390/atoms7030081

Authors: Oleksandr Marchuk Sven Dickheuer Stephan Ertmer Yuri Krasikov Philippe Mertens Christian Brandt Sebastijan Brezinsek Andrei Goriaev Mykola Ialovega Beatrix Göths Arkadi Kreter Christian Linsmeier

In this work, we present a new application for the line shapes of emission induced by reflected hydrogen atoms. Optical properties of the solids in contact with the plasma could be effectively measured at the wavelength of Balmer lines: time-resolved measurements of reflectance and polarization properties of mirrors are performed using the wavelength separation of the direct and reflected signals. One uses the Doppler effect of emission of atoms excited by collisions with noble gases, primarily with Ar or with Kr. In spite of a new application of line shapes, the question of the source of the strong signal in the case of Ar exists: the emission observed in the case of the excitation of H or D atoms by Ar exceeds the signal induced by collisions with Kr atoms by a factor of five, and the only available experimental data for the ground state excitation show practically equal cross-sections for both gases in the energy range of 80&ndash;200 eV.

]]>Atoms doi: 10.3390/atoms7030080

Authors: Magdalena Christova Milan S. Dimitrijević Sylvie Sahal-Bréchot

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

]]>Atoms doi: 10.3390/atoms7030079

Authors: Dimitrios Stefas Nikolaos Gyftokostas Elli Bellou Stelios Couris

In the present work, Laser-Induced Breakdown Spectroscopy (LIBS) is used for the discrimination/identification of different plastic/polymeric samples having the same polymeric matrix but containing different additives (as e.g., fillers, flame retardants, etc.). For the classification of the different plastic samples, some machine learning algorithms were employed for the analysis of the LIBS spectroscopic data, such as the Principal Component Analysis (PCA) and the Linear Discriminant Analysis (LDA). The combination of LIBS technique with these machine learning algorithmic approaches, in particular the latter, provided excellent classification results, achieving identification accuracies as high as 100%. It seems that machine learning paves the way towards the application of LIBS technique for identification/discrimination issues of plastics and polymers and eventually of other classes of organic materials. Machine learning assisted LIBS can be a simple to use, efficient and powerful tool for sorting and recycling purposes.

]]>Atoms doi: 10.3390/atoms7030078

Authors: Kanti M. Aggarwal

In a recent paper, Tayal et al. (Astrophys. J. Suppl. 2019, 242, 9) reported results for energy levels, radiative rates (A-values), and effective collision strengths ( &Upsilon; ) for transitions among the 198 levels of Si-like S III. For the calculations, they adopted the multi-configuration Hartree&ndash;Fock (MCHF) code for the energy levels and A-values and the B-spline R-matrix (BSR) code for &Upsilon; . Their reported results appear to be accurate for energy levels and A-values, but not for &Upsilon; . Through our independent calculations by adopting the flexible atomic code (FAC), we demonstrate that their reported results for &Upsilon; are underestimated, by up to a factor of two, and at all temperatures, particularly for the allowed transitions, but some forbidden ones as well. Additionally, for transitions involving the higher levels, the behaviour of their &Upsilon; results is not correct.

]]>Atoms doi: 10.3390/atoms7030077

Authors: Yasmina Ben Nana Fethi Khelfaoui Said Douis Eshrat Sadeghzadeh Lari Mohammed Tayeb Meftah

We investigate the ion effect on the broadening of the spectral line profile by the free electrons collisions with the emitters in plasmas. We only considered the weak collisions&rsquo; contribution. This effect has a consequence on the trajectories of the free electrons through the electric microfield created by the ions of the plasma. Thanks to the Meijer&rsquo;s functions, the calculation of the electronic Stark broadening is precisely established.

]]>Atoms doi: 10.3390/atoms7030076

Authors: Alberto Casado Santiago Guerra José Plácido

The Wigner formalism in the Heisenberg picture constitutes a bridge that connects Quantum Optics to Stochastic Optics. The vacuum field appears explicitly in the formalism, and the wavelike aspects of light are emphasised. In addition, the zeropoint intensity as a threshold for detection is a common denominator in both theories. In this paper, after summarising the basic rules of the Wigner approach and its application to parametric down-conversion, some new results are presented that delve into the physical meaning of the zeropoint field in optical quantum communication. Specifically, the relationship between Bell-state distinguishability and the number of sets of zeropoint modes that take part in the experiment is analysed in terms of the coupling between the phases of the different fields involved and the subtraction of the zeropoint intensity at the detectors. Additionally, the connection between the compatibility theorem in quantum cryptography and zeropoint field is stressed.

]]>Atoms doi: 10.3390/atoms7030075

Authors: Liam H. Scarlett Jeremy S. Savage Dmitry V. Fursa Mark C. Zammit Igor Bray

We present convergent close-coupling (CCC) calculations of electron-impact dissociation of vibrationally-excited molecular hydrogen into neutral fragments. This work follows from our previous results for dissociation of molecular hydrogen in the ground vibrational level [Scarlett et al., Eur. Phys. J. D 72, 34 (2018)], which were obtained from calculations performed in a spherical coordinate system. The present calculations, performed utilizing a spheroidal formulation of the molecular CCC method, reproduce the previous dissociation cross sections for the ground vibrational level, while allowing the extension to scattering on excited levels.

]]>Atoms doi: 10.3390/atoms7030074

Authors: Christian G. Parigger Christopher M. Helstern Ghaneshwar Gautam

In this study, we examine the atomic and molecular signatures in laser-induced plasma. Abel inversions of measured line-of-sight data reveal insight into the radial plasma distribution. Laser-plasma is generated with 6 ns, Q-switched Nd:YAG radiation with energies in the range of 100 to 800 mJ. Temporally- and spatially-resolved emission spectroscopy investigates expansion dynamics. Specific interests include atomic hydrogen (H) and cyanide (CN). Atomic hydrogen spectra indicate axisymmetric shell structures and isentropic expansion of the plasma kernel. The recombination radiation of CN emanates within the first 100 nanoseconds for laser-induced breakdown in a 1:1 mole ratio CO2:N2 gas mixture. CN excitation temperatures are determined from fitting recorded and computed spectra. Chemical equilibrium mole fractions of CN are computed for air and the CO2:N2 gas mixture. Measurements utilize a 0.64-m Czerny&ndash;Turner type spectrometer and an intensified charge-coupled device.

]]>Atoms doi: 10.3390/atoms7030073

Authors: Ashraf M. EL Sherbini Ahmed H. EL Farash Tharwat M. EL Sherbini Christian G. Parigger

Q-switched laser radiation at wavelengths of 355, 532, and 1064 nm from a Nd: YAG laser was used to generate plasma in laboratory air at the target surface made of nano-silver particles of size 95 &plusmn; 10 nm. The emitted resonance spectra from the neutral silver at wavelengths of 327.9 nm and 338.2 nm indicate existence of self-reversal in addition to plasma self-absorption. Both lines were identified in emission spectra at different laser irradiation wavelengths with characteristic dips at the un-shifted central wavelengths. These dips are usually associated with self-reversal. Under similar conditions, plasmas at the corresponding bulk silver target were generated. The recorded emission spectra were compared to those obtained from the nano-material target. The comparisons confirm existence of self-reversal of resonance lines that emerge from plasmas produced at nano-material targets. This work suggests a method for recovery of the spectral line shapes and discusses practical examples. In addition, subsidiary calibration efforts that utilize the Balmer series H&alpha;-line reveal that other Ag I lines at 827.35 nm and 768.7 nm are optically thin under variety of experimental conditions and are well-suited as reference lines for measurement of the laser plasma electron density.

]]>Atoms doi: 10.3390/atoms7030072

Authors: Abhishek K. Rai Jayanta K. Pati Christian G. Parigger Awadhesh K. Rai

The first detection of gypsum (CaSO4&middot;2H2O) by the Mars Science Laboratory (MSL) rover Curiosity in the Gale Crater, Mars created a profound impact on planetary science and exploration. The unique capability of plasma spectroscopy, which involves in situ elemental analysis in extraterrestrial environments, suggests the presence of water in the red planet based on phase characterization and provides a clue to Martian paleoclimate. The key to gypsum as an ideal paleoclimate proxy lies in its textural variants and terrestrial gypsum samples from varied locations and textural types have been analyzed with laser-induced breakdown spectroscopy (LIBS) in this study. Petrographic, sub-microscopic, and powder X-ray diffraction characterizations confirm the presence of gypsum (hydrated calcium sulphate; CaSO4&middot;2H2O), bassanite (semi-hydrated calcium sulphate; CaSO4&middot;&frac12;H2O), and anhydrite (anhydrous calcium sulphate; CaSO4), along with accessory phases (quartz and jarosite). The principal component analysis of LIBS spectra from texturally varied gypsums can be differentiated from one another due to the chemical variability in their elemental concentrations. The concentration of gypsum is determined from the partial least-square regressions model. The rapid characterization of gypsum samples with LIBS is expected to work well in extraterrestrial environments.

]]>Atoms doi: 10.3390/atoms7030071

Authors: Pravin Kumar Tiwari Nilesh Kumar Rai Rohit Kumar Christian G. Parigger Awadhesh Kumar Rai

Laser-induced breakdown spectroscopy (LIBS) of pharmaceutical drugs that contain paracetamol was investigated in air and argon atmospheres. The characteristic neutral and ionic spectral lines of various elements and molecular signatures of CN violet and C2 Swan band systems were observed. The relative hardness of all drug samples was measured as well. Principal component analysis, a multivariate method, was applied in the data analysis for demarcation purposes of the drug samples. The CN violet and C2 Swan spectral radiances were investigated for evaluation of a possible correlation of the chemical and molecular structures of the pharmaceuticals. Complementary Raman and Fourier-transform-infrared spectroscopies were used to record the molecular spectra of the drug samples. The application of the above techniques for drug screening are important for the identification and mitigation of drugs that contain additives that may cause adverse side-effects.

]]>Atoms doi: 10.3390/atoms7030070

Authors: Jen-Hao Ou Yew Kam Ho

Knowledge of the electronic structures of atomic and molecular systems deepens our understanding of the desired system. In particular, several information-theoretic quantities, such as Shannon entropy, have been applied to quantify the extent of electron delocalization for the ground state of various systems. To explore excited states, we calculated Shannon entropy and two of its one-parameter generalizations, R&eacute;nyi entropy of order &alpha; and Tsallis entropy of order &alpha; , and Onicescu Information Energy of order &alpha; for four low-lying singly excited states (1s2s 1 S e , 1s2s 3 S e , 1s3s 1 S e , and 1s3s 3 S e states) of helium. This paper compares the behavior of these three quantities of order 0.5 to 9 for the ground and four excited states. We found that, generally, a higher excited state had a larger R&eacute;nyi entropy, larger Tsallis entropy, and smaller Onicescu information energy. However, this trend was not definite and the singlet&ndash;triplet reversal occurred for R&eacute;nyi entropy, Tsallis entropy and Onicescu information energy at a certain range of order &alpha; .

]]>Atoms doi: 10.3390/atoms7030069

Authors: A.K. Bhatia

The excitation cross-sections of the 2S state of atomic hydrogen at low (near threshold energy) to high incident positron energies (10.30 to 300 eV) have been calculated using the variational polarized-orbital method. Nine partial waves have been used to obtain converged cross-sections in the above energy range. The cross sections compared to the electron-impact excitation of the S state of atomic hydrogen are larger in the present case. The maximum cross section is 3.63(&minus;1) &pi; a 0 2 at 16.5 eV compared to 1.37(&minus;1) &pi; a 0 2 at 11.14 eV for the electron-impact excitation. The present results are compared with other calculations. Cross-sections have also been calculated in the Born approximation in which the polarization of the target has been included. Differential cross sections were calculated at k = 1.0 (13.6eV), 2.5 (85 eV), 3.483 (200 3V), and 4.696 (300 eV).

]]>Atoms doi: 10.3390/atoms7030068

Authors: Eugene Oks

The author wishes to make the following corrections to this paper [...]

]]>Atoms doi: 10.3390/atoms7030067

Authors: Mehdi Ayouz Viatcheslav Kokoouline

Cross sections and thermal rate coefficients for rotational and vibration excitation of the four stable isotopologues of the 4 HeH + ion by electron impact are presented. The data are calculated using a previously developed theoretical approach. The obtained rate coefficients are fitted to analytical formulas with the 10&ndash;10,000 K interval of applicability. These present results could be useful in tokamak plasma and astrophysical modeling and can help in the detection of these species in the interstellar medium.

]]>Atoms doi: 10.3390/atoms7030066

Authors: Chihiro Suzuki Fumihiro Koike Izumi Murakami Naoki Tamura Shigeru Sudo Gerry O’Sullivan

Soft X-ray spectra from high Z rare-earth (lanthanide) elements have been systematically observed in optically thin, high-temperature plasmas produced in the Large Helical Device (LHD), a facility for magnetically confined fusion research. It has been demonstrated that the discrete and quasicontinuum (UTA) spectral features from highly charged lanthanide ions are observed depending on the plasma temperature. The analyses of the measured spectra are ongoing by comparisons with theoretical calculations and/or previous experimental data available. The discrete spectra recorded in high-temperature conditions are dominated by individual lines of Ge- to Ni-like ions, while prominent peaks in the narrowed UTA spectra observed in low-temperature conditions are well explained by the transitions of Ag- to Rh-like ions.

]]>Atoms doi: 10.3390/atoms7030065

Authors: Brian K. Kendrick N. Balakrishnan

The role of the geometric phase effect in chemical reaction dynamics has long been a topic of active experimental and theoretical investigations. The topic has received renewed interest in recent years in cold and ultracold chemistry where it was shown to play a decisive role in state-to-state chemical dynamics. We provide a brief review of these developments focusing on recent studies of O + OH and hydrogen exchange in the H + H 2 and D + HD reactions at cold and ultracold temperatures. Non-adiabatic effects in ultracold chemical dynamics arising from the conical intersection between two electronic potential energy surfaces are also briefly discussed. By taking the hydrogen exchange reaction as an illustrative example it is shown that the inclusion of the geometric phase effect captures the essential features of non-adiabatic dynamics at collision energies below the conical intersection.

]]>Atoms doi: 10.3390/atoms7030064

Authors: Alexander Kramida

The famous Cowan&rsquo;s book, &ldquo;The Theory of Atomic Structure and Spectra&rdquo;, published in 1981, and his suite of computer codes based on it, continue to be highly influential in atomic physics and many other research areas. As of September 2018, there have been more than 5000 citations to Cowan&rsquo;s book and codes, and each year adds about 150 citations to this list. The present work briefly describes what these codes do and why they are responsible for most of the current progress in the analyses of atomic spectra. Various modifications of these codes, including my own, will also be described.

]]>Atoms doi: 10.3390/atoms7030063

Authors: Christian G. Parigger Christopher M. Helstern Ghaneshwar Gautam

This work discusses laboratory measurements of atomic and diatomic molecular species in laser-plasma generated in gases. Noticeable self-absorption of the Balmer series hydrogen alpha line occurs for electron densities of the order of one tenth of standard ambient temperature and pressure density. Emission spectra of selected diatomic molecules in air or specific gaseous mixtures at or near atmospheric pressure reveal minimal plasma re-absorption. Abel inversion of the plasma in selected gases and gas mixtures confirm expansion dynamics that unravel regions of atomic and molecular species of different electron temperature and density. Time resolved spectroscopy diagnoses self-absorption of hydrogen alpha and hydrogen beta lines in ultra-high pure hydrogen gas. Radiation from a Nd:YAG laser device induces micro-plasma for pulse widths in the range of 6&ndash;14 ns, energies in the range of 100&ndash;800 mJ, and peak irradiances of the order 1&ndash;10 TW/cm 2 . Atomic line profiles yield electron density and temperature from fitting of line profiles to wavelength and sensitivity corrected spectral radiance data. Analysis of measured diatomic emission data yields excitation temperature of primarily molecular recombination spectra. Applications of the laboratory experiments extend to investigations of stellar astrophysics white dwarf spectra.

]]>Atoms doi: 10.3390/atoms7030062

Authors: A. V. Kudrin A. Zaitsevskii T. A. Isaev D. E. Maison L. V. Skripnikov

Molecular properties of the thallium monocyanide (Tl&middot;CN) system in its ground electronic state are studied using high-precision ab initio relativistic two-component pseudopotential replacing 60 inner-core electrons of Tl. A relativistic coupled-cluster method with single, double and perturbative triple amplitudes is employed to account for electronic correlations. Extrapolation of results to the complete basis set limit is used for all studied properties. The global potential energy minimum of Tl&middot;CN corresponds to the linear cyanide (TlCN) isomer, while the non-rigid isocyanide-like (TlNC) structure lies by approximately 11 kJ/mol higher in energy. The procedure of restoration of the wavefunction in the &ldquo;core&rdquo; region of Tl atom was applied to calculate the interaction of the Tl nuclear Schiff moment with electrons. The parameter X of the interaction of the Tl nuclear Schiff moment with electrons in the linear TlCN molecule equals 7150 a.u. The prospects of using the TlCN molecule for the experimental detection of the nuclear Schiff moment are discussed.

]]>Atoms doi: 10.3390/atoms7030061

Authors: Christian G. Parigger

This work communicates laser-plasma experiments in a gaseous mixture of hydrogen and nitrogen. Time-resolved spectroscopy measures the first four Balmer-series hydrogen lines together with selected neutral and ionized nitrogen lines. Optical breakdown plasma is generated in a 1:1 hydrogen:nitrogen mixture at ambient temperature and 0.27-atm pressure. Time-resolved spectroscopy records emitted radiation with spatial resolution along the slit height for the H &alpha; , H &beta; , H &gamma; , and H &delta; lines. For 13 selected time delays from 0.25 &mu; s to 3.25 &mu; s and 0.025 &mu; s gate-widths, micro-plasma diagnostics is evaluated. Of interest are the peak separation and width of H &delta; and width of H &gamma; for electron densities in the range of 0.1 to 1.0 &times; 10 17 cm &minus; 3 , and comparisons with H &beta; and H &alpha; diagnostics. Integral inversions interrogate spatial distributions of the plasma expansion. Applications include laboratory and stellar astrophysics plasma diagnosis.

]]>Atoms doi: 10.3390/atoms7030060

Authors: Yogesh Kumar Manoj Kumar Sachin Kumar Rajeev Kumar

In the present investigation, the plane-wave Born approximation was employed to calculate the total ionization cross sections by electron impact of methanol, ethanol and 1-propanol from the threshold of ionization to 10 MeV. This method requires continuum generalized oscillator strengths (CGOSs). The two different semi-phenomenological expressions of CGOS, given by Mayol and Salvat and Weizsacker and Williams, along with approximated form of the continuum optical oscillator strength (COOS) by Khare et al. were used. Furthermore, the average of the above two CGOSs was also used. The calculated ionization cross sections were compared to the available previous theoretical results and experimental data. Out of three CGOSs, the present results with the average CGOS were found in good agreement with the available experimental results for all the considered molecules. Collision parameters CRP were also calculated from 0.1 to 100 MeV and the calculations were found to be in excellent agreement with the experimental results of Reike and Prepejchal.

]]>Atoms doi: 10.3390/atoms7020059

Authors: Theodorus Maria Nieuwenhuizen

In this paper, the harmonic oscillator problem in Stochastic Electrodynamics is revisited. Using the exact shape of the Lorentz damping term prevents run-away effects. After introducing a cut-off in the stochastic power spectrum and regularizing the stochastic force, all relevant integrals are dominated by resonance effects only and results are derived that stem from those in the quantum ground state. For an orbit with specific position and momentum at an initial time, the average energy and the average rate of energy change are evaluated, which stem with each other. Resonance effects are highlighted along the way. An outlook on the hydrogen ground state problem is provided.

]]>Atoms doi: 10.3390/atoms7020058

Authors: V. S. Prasannaa A. Sunaga M. Abe M. Hada N. Shitara A. Sakurai B. P. Das

In this review article, we survey some of our results pertaining to the search for the electric dipole moment of the electron (eEDM), using heavy polar molecules. In particular, we focus on the relativistic coupled cluster method (RCCM) and its applications to eEDM searches in YbF, HgX (X = F, Cl, Br, and I), BaF, HgA (A = Li, Na, and K), and YbOH. Our results are presented in a systematic manner, by first introducing the eEDM and its measurement using molecules, the importance of relativistic many-body theory, and finally our results, followed by future prospects.

]]>Atoms doi: 10.3390/atoms7020057

Authors: Beatrice Campanella Stefano Legnaioli Stefano Pagnotta Francesco Poggialini Vincenzo Palleschi

The production of a plasma by a pulsed laser beam in solids, liquids or gas is often associated with the generation of a strong shock wave, which can be studied and interpreted in the framework of the theory of strong explosion. In this review, we will briefly present a theoretical interpretation of the physical mechanisms of laser-generated shock waves. After that, we will discuss how the study of the dynamics of the laser-induced shock wave can be used for obtaining useful information about the laser&ndash;target interaction (for example, the energy delivered by the laser on the target material) or on the physical properties of the target itself (hardness). Finally, we will focus the discussion on how the laser-induced shock wave can be exploited in analytical applications of Laser-Induced Plasmas as, for example, in Double-Pulse Laser-Induced Breakdown Spectroscopy experiments.

]]>Atoms doi: 10.3390/atoms7020056

Authors: Dmitry V. Chubukov Leonid V. Skripnikov Vasily N. Kutuzov Sergey D. Chekhovskoi Leonti N. Labzowsky

The P , T -odd Faraday effect (i.e., rotation of the polarization plane of light propagating through a medium in presence of the external electric field due to P , T symmetry violating interactions) is considered for several atomic species: Ra, Pb, Tl, Hg, Cs, and Xe. Corresponding theoretical simulation of P , T -odd Faraday experiment, with already achieved intracavity absorption spectroscopy characteristics and parameters, is performed. The results show that the magnetic dipole transitions in the Tl and Pb atoms as well as the electric dipole transitions in the Ra, Hg and Cs atoms are favorable for the observation of the P , T -odd Faraday optical rotation. The estimation of the rotation angle of the light polarization plane demonstrates that recently existing boundaries for the electron electric dipole moment can be improved by one-two orders of magnitude.

]]>Atoms doi: 10.3390/atoms7020055

Authors: Motoshi Goto Ryohko Ishikawa Yusuke Iida Saku Tsuneta

We have solved a problem of the Hanle effect for the hydrogen Lyman- &alpha; line in an intuitive and straightforward way. The Stokes parameters amid an anisotropic radiation field and a magnetic field are derived as an analytical formula which enables us to conduct immediate analyses of observation data taken by spectro-polarimetry. The derived formula is, in particular, supposed to be used for the analysis of the data taken by CLASP (Chromospheric Lyman-Alpha Spectro-Polarimeter), which has aimed at measuring the linear polarization in the hydrogen Lyman- &alpha; line (121.6 nm) and then evaluating the magnetic field in the upper chromosphere and the transition region. The dependence of the Stokes parameters on the strength and direction of the magnetic field and on the observation angle is derived with our analytical model. The results show a satisfactory agreement with those of a more rigorous numerical calculation where the radiative transfer is taken into account and the consistency is assured between the anisotropic randiation field and the polarized atomic state.

]]>Atoms doi: 10.3390/atoms7020054

Authors: Charlotte Froese Fischer James F. Babb

Fully relativistic calculations have been performed for two multiplets, 3 s 3 p 2 4 P and 3 s 3 p 4 s 4 P o , in Al i. Wave functions were obtained for all levels of these multiplets using the grasp programs. Reported are the E1 transitions rates for all transitions between levels of these multiplets. Transition energies and transition rates are compared with observed values and other theory. Our calculated transition rates are smaller by about 10% than observed rates, reducing a large discrepancy between earlier calculations and experiments.

]]>Atoms doi: 10.3390/atoms7020053

Authors: Sabyasachi Kar Yu-Shu Wang Yang Wang Yew Kam Ho

The question of stability of a given quantum system made up of charged particles is of fundamental interest in atomic, molecular, and nuclear physics. In this work, the stability for the negatively charged positronium (Ps)-like ions or the three-body system ( Z e + , e &minus; , e &minus; ) with Yukawa potentials is studied using correlated exponential wavefunctions based on the Ritz variational method. We obtained the critical screening parameter &mu; C as a function of the continuously varied nuclear charge Z , the critical nuclear charge Z C as a function of the screening parameter &mu; , and the ionization energies in terms of the screening parameter &mu; and Z . The critical nuclear charge for the bare Coulomb system ( Z e + , e &minus; , e &minus; ) obtained using 700-term correlated exponential wavefunctions is in accord with the reported results. The ionization energy, &mu; C , and Z C for the Yukawa system ( Z e + , e &minus; , e &minus; ) exhibit interesting behaviors. The present study describes the possible nonexistence of Borromean binding as well as Efimov states. The possible existence of quasi-bound resonances states for the negatively charged screened Ps-like ions is briefly discussed.

]]>Atoms doi: 10.3390/atoms7020052

Authors: Spiros Alexiou

In recent work, the effect of a magnetic field on the line shapes via the modification of electron perturber trajectories was considered. In the present paper we revisit this idea using a variation of the Collision-time Statistics method, in order to account for a l l relevant perturbers. We also obtain line profiles for the hydrogen L &alpha; line for conditions of astrophysical interest. Although the Collision-time statistics method works for both electrons and ions, we apply a simplification here that results in an excessive number of ions having to be simulated. As a result, the present, simplified version, is typically only appropriate for electrons.

]]>Atoms doi: 10.3390/atoms7020051

Authors: Garret Moddel Olga Dmitriyeva

In research articles and patents several methods have been proposed for the extraction of zero-point energy from the vacuum. None of the proposals have been reliably demonstrated, yet they remain largely unchallenged. In this paper the underlying thermodynamics principles of equilibrium, detailed balance, and conservation laws are presented for zero-point energy extraction. The proposed methods are separated into three classes: nonlinear processing of the zero-point field, mechanical extraction using Casimir cavities, and the pumping of atoms through Casimir cavities. The first two approaches are shown to violate thermodynamics principles, and therefore appear not to be feasible, no matter how innovative their execution. The third approach, based upon stochastic electrodynamics, does not appear to violate these principles, but may face other obstacles. Initial experimental results are tantalizing but, given the lower than expected power output, inconclusive.

]]>Atoms doi: 10.3390/atoms7020050

Authors: Daniel C. Cole

The zero-point (ZP) radiation field in stochastic electrodynamics (SED) is considered to be formally infinite, or perhaps bounded by mechanisms yet to be revealed someday. A similar situation holds in quantum electrodynamics (QED), although there the ZP field is considered to be &ldquo;virtual&rdquo;. The first part of this article addresses the concern by some about the related disturbing concept of &ldquo;extracting energy&rdquo; from this formally, enormous source of energy. The second part of this article introduces a new method for calculating probabilities of fields in SED, which can be extended to linear oscillators in SED.

]]>Atoms doi: 10.3390/atoms7020049

Authors: Akira Ueda Taiichi Shikama Yohei Iida Masahiro Hasuo

Production of a plasma that has a large degree of ionization (DOI), volume, and spatial and temporal uniformities is a challenge for the improvement of the performance of plasma-based vapor deposition processes. As a potential candidate for the discharge, we investigate plasma parameters arising in helium electron cyclotron resonance (ECR) discharges due to a simple cusp field. Two-dimensional distributions of helium atom emission-line intensities were measured using spectroscopy with multiple viewing chords and then de-convoluted by Abel inversion. The local plasma parameters, including the atomic density, were evaluated using collisional-radiative model analysis. The DOI calculated from the electron and atomic densities reached up to 35% and, in most of the region inside the ECR surface, it was more than 10%.

]]>Atoms doi: 10.3390/atoms7020048

Authors: Sven Dickheuer Oleksandr Marchuk Tsanko Vaskov Tsankov Dirk Luggenhölscher Uwe Czarnetzki Wojciech Gromelski Stephan Ertmer Arkadi Kreter

Tunable diode laser absorption spectroscopy (TDLAS) is a commonly used technique to measure the temperature and density of atoms or molecules in a gas. In this work, we demonstrate that the TDLAS diagnostics could be effectively applied to measure the magnetic field in a low-density weakly magnetized plasma using the Zeeman splitting of the absorption spectrum of lines from noble gases. The laser wavelength is tailored to fit the 1 s 5 &rarr; 2 p 6 transition of atomic Ar with the wavelength &lambda; = 763.51 nm . Two mechanisms of line broadening and splitting are observed: Doppler broadening and Zeeman effect. The latter is especially pronounced by applying polarization-selective observation of the absorption to the TDLAS measurements. By fitting the &sigma; and &pi; components of the absorption spectrum, the line-integrated magnetic field on the order of 30&ndash;50 mT is determined. The agreement between the measured values and the vacuum field (neglecting the impact of the plasma) calculations on the axis of the PSI-2 is found to be about 15&ndash;20%.

]]>Atoms doi: 10.3390/atoms7020047

Authors: Robert Beuc Mladen Movre Berislav Horvatić

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

]]>Atoms doi: 10.3390/atoms7020046

Authors: Andrea Valdés-Hernández Ana María Cetto Luis de la Peña

The correlation of projections of the momentum operators of two particles is used to derive a quantum inequality for continuous variables, which must be satisfied by any bipartite system in a pure state. This inequality resembles a Clauser&ndash;Horne&ndash;Shimony&ndash;Holt (CHSH)-type inequality except for additional terms related to the imaginary component of the weak value of the momentum, which normally remains concealed in the usual quantum description but turns out to be of relevance for entangled states. Our results shed new light on the link between noncommutativity, entanglement and nonlocality of the quantum description.

]]>Atoms doi: 10.3390/atoms7020045

Authors: G. Gabrielse S. E. Fayer T. G. Myers X. Fan

The electron and positron magnetic moments are the most precise prediction of the standard model of particle physics. The most accurate measurement of a property of an elementary particle has been made to test this result. A new experimental method is now being employed in an attempt to improve the measurement accuracy by an order of magnitude. Positrons from a &ldquo;student source&rdquo; now suffice for the experiment. Progress toward a new measurement is summarized.

]]>Atoms doi: 10.3390/atoms7020044

Authors: Allison Harris

Differential cross sections (DCS) for single electron capture from helium by heavy ion impact are calculated using a frozen core 3-body model and an active electron 4-body model within the first Born approximation. DCS are presented for H+, He2+, Li3+, and C6+ projectiles with velocities of 1 MeV/amu and 10 MeV/amu. In general, the DCS from the two models are found to differ by about one to two orders of magnitude with the active electron 4-body model showing better agreement with experiment. Comparison of the models reveals two possible sources of the magnitude difference: the inactive electron&rsquo;s change of state and the projectile&ndash;target Coulomb interaction used in the different models. Detailed analysis indicates that the uncaptured electron&rsquo;s change of state can safely be neglected in the frozen core approximation, but that care must be used in modeling the projectile&ndash;target interaction.

]]>Atoms doi: 10.3390/atoms7020043

Authors: Antônio M. S. Macêdo Iván R. Roa González Ernesto P. Raposo Leonardo de S. Menezes Anderson S. L. Gomes

In fluid turbulence, intermittency is the emergence of non-Gaussian tails in the distribution of velocity increments in small space and/or time scales. Intermittence is thus expected to gradually disappear as one moves from small to large scales. Here we study the turbulent-like intermittency effect experimentally observed in the distribution of intensity fluctuations in a disordered continuous-wave-pumped erbium-doped-based random fiber laser with specially-designed random fiber Bragg gratings. The intermittency effect is investigated as a crossover in the distribution of intensity increments from a heavy-tailed distribution (for short time scales), to a Gaussian distribution (for large time scales). The results are theoretically supported by a hierarchical stochastic model that incorporates Kolmogorov&rsquo;s theory of turbulence. In particular, the discrete version of the hierachical model allows a general direct interpretation of the number of relevant scales in the photonic hierarchy as the order of the transitions induced by the non-linearities in the medium. Our results thus provide further statistical evidence for the interpretation of the turbulence-like emission previously observed in this system.

]]>Atoms doi: 10.3390/atoms7020042

Authors: Wayne Cheng-Wei Huang Herman Batelaan

The interference pattern in electron double-slit diffraction is a hallmark of quantum mechanics. A long-standing question for stochastic electrodynamics (SED) is whether or not it is capable of reproducing such effects, as interference is a manifestation of quantum coherence. In this study, we used excited harmonic oscillators to directly test this quantum feature in SED. We used two counter-propagating dichromatic laser pulses to promote a ground-state harmonic oscillator to a squeezed Schr&ouml;dinger cat state. Upon recombination of the two well-separated wavepackets, an interference pattern emerges in the quantum probability distribution but is absent in the SED probability distribution. We thus give a counterexample that rejects SED as a valid alternative to quantum mechanics.

]]>Atoms doi: 10.3390/atoms7020041

Authors: Sunny Vagnozzi

In the past years, a systematic downward revision of the metallicity of the Sun has led to the &ldquo;solar modeling problem&rdquo;, namely the disagreement between predictions of standard solar models and inferences from helioseismology. Recent solar wind measurements of the metallicity of the Sun, however, provide once more an indication of a high-metallicity Sun. Because of the effects of possible residual fractionation, the derived value of the metallicity Z ⊙ = 0.0196 &plusmn; 0.0014 actually represents a lower limit to the true metallicity of the Sun. However, when compared with helioseismological measurements, solar models computed using these new abundances fail to restore agreement, owing to the implausibly high abundance of refractory (Mg, Si, S, Fe) elements, which correlates with a higher core temperature and hence an overproduction of solar neutrinos. Moreover, the robustness of these measurements is challenged by possible first ionization potential fractionation processes. I will discuss these solar wind measurements, which leave the &ldquo;solar modeling problem&rdquo; unsolved.

]]>Atoms doi: 10.3390/atoms7020040

Authors: Abdelkader Makhoute Driss Khalil Imane Ajana

In this review, we present a comprehensive survey of laser-assisted (e, 2e) reactions. The influence of a laser field on the dynamics of (e, 2e) collisions in atomic hydrogen is analyzed in the symmetric and asymmetric coplanar geometries. Particular attention is devoted to the construction of the dressed (laser-modified) target wave functions, in both the initial and final states. The calculation is performed in the framework of Coulomb-Volkov-Born approximation, where the initial and final electrons are described by Volkov wave functions, while the interaction of the incident electron with the target atom is treated in the first and the second Born approximation. The state of the ejected electron is described by a Volkov/Coulomb-Volkov wave function. A detailed account is also given of the techniques we have used to evaluate the scattering amplitudes. The influence of the laser parameters (frequency, intensity, and direction of polarization) on the angular distribution of the ejected electron is discussed, and a number of illustrative examples are given. The structure of the triple differential cross section in the vicinity of resonances is also analyzed.

]]>Atoms doi: 10.3390/atoms7020039

Authors: G. Jordan Maclay

Stochastic Electrodynamics (SED) has had success modeling black body radiation, the harmonic oscillator, the Casimir effect, van der Waals forces, diamagnetism, and uniform acceleration of electrodynamic systems using the stochastic zero-point fluctuations of the electromagnetic field with classical mechanics. However the hydrogen atom, with its 1/r potential remains a critical challenge. Numerical calculations have shown that the SED field prevents the electron orbit from collapsing into the proton, but, eventually the atom becames ionized. We look at the issues of the H atom and SED from the perspective of symmetry of the quantum mechanical Hamiltonian, used to obtain the quantum mechanical results, and the Abraham-Lorentz equation, which is a force equation that includes the effects of radiation reaction, and is used to obtain the SED simulations. We contrast the physical computed effects of the quantized electromagnetic vacuum fluctuations with the role of the real stochastic electromagnetic field.

]]>Atoms doi: 10.3390/atoms7010038

Authors: Sébastien Gamrath Patrick Palmeri Pascal Quinet

Calculated radiative transition probabilities and oscillator strengths are reported for 392 lines of neutral lanthanum (La I) atom in the spectral range from the near ultraviolet to the mid infrared. They were obtained using two different theoretical methods based on the pseudo-relativistic Hartree&ndash;Fock (HFR) and the fully relativistic multiconfiguration Dirac&ndash;Hartree&ndash;Fock (MCDHF) approaches, both including the most important intravalence and core-valence electron correlations. The quality of these radiative parameters was assessed through detailed comparisons between the results obtained using different physical models and between our theoretical results and the experimental data, where available. Of the total number of La I lines listed in the present work, about 60% have gf- and gA-values determined for the first time.

]]>Atoms doi: 10.3390/atoms7010037

Authors: Edmund G. Myers

Atomic mass measurements are essential for obtaining several of the fundamental constants. The most precise atomic mass measurements, at the 10&minus;10 level of precision or better, employ measurements of cyclotron frequencies of single ions in Penning traps. We discuss the relation of atomic masses to fundamental constants in the context of the revised SI. We then review experimental methods, and the current status of measurements of the masses of the electron, proton, neutron, deuteron, tritium, helium-3, helium-4, oxygen-16, silicon-28, rubidium-87, and cesium-133. We conclude with directions for future work.

]]>Atoms doi: 10.3390/atoms7010036

Authors: Hui Li Ming Li Constantinos Makrides Alexander Petrov Svetlana Kotochigova

Universal collisions describe the reaction of molecules and atoms as dominated by long-range interparticle interactions. Here, we calculate the universal inelastic rate coefficients for a large group of ultracold polar molecules in their lower ro-vibrational states colliding with one of their constituent atoms. The rate coefficients are solely determined by values of the dispersion coefficient and reduced mass of the collisional system. We use the ab initio coupled-cluster linear response method to compute dynamic molecular polarizabilities and obtain the dispersion coefficients for some of the collisional partners and use values from the literature for others. Our polarizability calculations agree well with available experimental measurements. Comparison of our inelastic rate coefficients with results of numerically exact quantum-mechanical calculations leads us to conjecture that collisions with heavier atoms can be expected to be more universal.

]]>Atoms doi: 10.3390/atoms7010035

Authors: Mark E. Koepke

The objectives of this review are to articulate geospace, heliospheric, and astrophysical plasma physics issues that are addressable by laboratory experiments, to convey the wide range of laboratory experiments involved in this interdisciplinary alliance, and to illustrate how lab experiments on the centimeter or meter scale can develop, through the intermediary of a computer simulation, physically credible scaling of physical processes taking place in a distant part of the universe over enormous length scales. The space physics motivation of laboratory investigations and the scaling of laboratory plasma parameters to space plasma conditions, having expanded to magnetic fusion and inertial fusion experiments, are discussed. Examples demonstrating how laboratory experiments develop physical insight, validate or invalidate theoretical models, discover unexpected behavior, and establish observational signatures for the space community are presented. The various device configurations found in space-related laboratory investigations are outlined.

]]>Atoms doi: 10.3390/atoms7010034

Authors: Felipe Cajiao Vélez Jerzy Z. Kamiński Katarzyna Krajewska

The theoretical analysis of four fundamental laser-assisted non-linear scattering processes are summarized in this review. Our attention is focused on Thomson, Compton, M&oslash;ller and Mott scattering in the presence of intense electromagnetic radiation. Depending on the phenomena under considerations, we model the laser field as a single laser pulse of ultrashort duration (for Thomson and Compton scattering) or non-monochromatic trains of pulses (for M&oslash;ller and Mott scattering).

]]>Atoms doi: 10.3390/atoms7010033

Authors: Jan Hendrik Bredehöft

Electron&ndash;molecule interactions have been studied for a long time. Most of these studies have in the past been limited to the gas phase. In the condensed-phase processes that have recently attracted attention from academia as well as industry, a theoretical understanding is mostly based on electron&ndash;molecule interaction data from these gas phase experiments. When transferring this knowledge to condensed-phase problems, where number densities are much higher and multi-body interactions are common, care must be taken to critically interpret data, in the light of this chemical environment. The paper presented here highlights three typical challenges, namely the shift of ionization energies, the difference in absolute cross-sections and branching ratios, and the occurrence of multi-body processes that can stabilize otherwise unstable intermediates. Examples from recent research in astrochemistry, where radiation driven chemistry is imminently important are used to illustrate these challenges.

]]>Atoms doi: 10.3390/atoms7010032

Authors: Christophe Blondel David Bresteau Cyril Drag

Neutral beam injection, for plasma heating, will supposedly be achieved, in ITER, by collisional detachment of a pre-accelerated D − beam. Collisional detachment, however, makes use of a D 2 -filled neutralisation chamber, which has severe drawbacks, including the necessity to set the D − -ion source at −1 MV. Photodetachment, in contradistinction, would have several advantages as a neutralisation method, including the absence of gas injection, and the possibility to set the ion source close to the earth potential. Photodetachment, however, requires a very high laser flux. The presented work has consisted in implementing an optical cavity, with a finesse greater than 3000, to make such a high illumination possible with a state-of-the-art CW (continuous-wave) laser. A 1.2 keV 1 H − -beam (only 20 times slower than the 1 MeV 2 D − ion beams to be prepared for ITER) was photodetached with more-than-50% efficiency, with only 24 W of CW laser input. This experimental demonstration paves the way for developing real-size photoneutralizers, based on the implementation of refolded optical cavities around the ion beams of neutral beam injectors. Depending on whether the specifications of the laser power or the cavity finesse will be more difficult to achieve in real scale, different architectures can be considered, with greater or smaller numbers of optical refoldings or (inclusively) optical cavities in succession, on the beam to be neutralised.

]]>Atoms doi: 10.3390/atoms7010030

Authors: Manfred von Hellermann Maarten de Bock Oleksandr Marchuk Detlev Reiter Stanislav Serov Michael Walsh

The concept and structure of the Simulation of Spectra (SOS) code is described starting with an introduction to the physics background of the project and the development of a simulation tool enabling the modeling of charge-exchange recombination spectroscopy (CXRS) and associated passive background spectra observed in hot fusion plasmas. The generic structure of the code implies its general applicability to any fusion device, the development is indeed based on over two decades of spectroscopic observations and validation of derived plasma data. Four main types of active spectra are addressed in SOS. The first type represents thermal low-Z impurity ions and the associated spectral background. The second type of spectra represent slowing-down high energy ions created from either thermo-nuclear fusion reactions or ions from injected high energy neutral beams. Two other modules are dedicated to CXRS spectra representing bulk plasma ions (H+, D+, or T+) and beam emission spectroscopy (BES) or Motional Stark Effect (MSE) spectrum appearing in the same spectral range. The main part of the paper describes the physics background for the underlying emission processes: active and passive CXRS emission, continuum radiation, edge line emission, halo and plume effect, or finally the charge exchange (CX) cross-section effects on line shapes. The description is summarized by modeling the fast ions emissions, e.g., either of the &alpha; particles of the fusion reaction or of the beam ions itself.

]]>Atoms doi: 10.3390/atoms7010031

Authors: Francisco Navarrete Raúl Barrachina Marcelo F. Ciappina

We analyze the influence of the coherence of the projectile&rsquo;s beam in scattering phenomena. We focus our study in the ionization of He by C 6 + projectiles at 100 MeV/amu. We assess the influence of this effect by performing a Born initial state and continuum distorted wave final state (CDW-B1) calculation together with a rigorous procedure to account for the initial coherence properties of the projectile&rsquo;s beam. These calculations, which had been previously performed for only the scattering and perpendicular collision planes and within the First Born approximation (FBA), were repeated for an ampler set of collision planes. Additionally, a more refined method to describe the applicability of the aforementioned procedure, is used. We achieve a better qualitative agreement with the experimental results.

]]>Atoms doi: 10.3390/atoms7010029

Authors: Timothy H. Boyer

Stochastic electrodynamics is the classical electrodynamic theory of interacting point charges which includes random classical radiation with a Lorentz-invariant spectrum whose scale is set by Planck&rsquo;s constant. Here, we give a cursory overview of the basic ideas of stochastic electrodynamics, of the successes of the theory, and of its connections to quantum theory.

]]>Atoms doi: 10.3390/atoms7010028

Authors: Tatsumi Aoyama Toichiro Kinoshita Makiko Nio

The anomalous magnetic moment of the electron a e measured in a Penning trap occupies a unique position among high precision measurements of physical constants in the sense that it can be compared directly with the theoretical calculation based on the renormalized quantum electrodynamics (QED) to high orders of perturbation expansion in the fine structure constant &alpha; , with an effective parameter &alpha; / &pi; . Both numerical and analytic evaluations of a e up to ( &alpha; / &pi; ) 4 are firmly established. The coefficient of ( &alpha; / &pi; ) 5 has been obtained recently by an extensive numerical integration. The contributions of hadronic and weak interactions have also been estimated. The sum of all these terms leads to a e ( theory ) = 1 159 652 181.606 ( 11 ) ( 12 ) ( 229 ) &times; 10 &minus; 12 , where the first two uncertainties are from the tenth-order QED term and the hadronic term, respectively. The third and largest uncertainty comes from the current best value of the fine-structure constant derived from the cesium recoil measurement: &alpha; &minus; 1 ( Cs ) = 137.035 999 046 ( 27 ) . The discrepancy between a e ( theory ) and a e ( ( experiment ) ) is 2.4 &sigma; . Assuming that the standard model is valid so that a e (theory) = a e (experiment) holds, we obtain &alpha; &minus; 1 ( a e ) = 137.035 999 1496 ( 13 ) ( 14 ) ( 330 ) , which is nearly as accurate as &alpha; &minus; 1 ( Cs ) . The uncertainties are from the tenth-order QED term, hadronic term, and the best measurement of a e , in this order.

]]>Atoms doi: 10.3390/atoms7010027

Authors: Ralf Menzel Axel Heuer Peter W. Milonni

Using two crystals for spontaneous parametric down-conversion in a parallel setup, we observe two-photon interference with high visibility. The high visibility is consistent with complementarity and the absence of which-path information. The observations are explained as the effects of entanglement or equivalently in terms of interfering probability amplitudes and also by the calculation of a second-order field correlation function in the Heisenberg picture. The latter approach brings out explicitly the role of the vacuum fields in the down-conversion at the crystals and in the photon coincidence counting. For comparison, we show that the Hong&ndash;Ou&ndash;Mandel dip can be explained by the same approach in which the role of the vacuum signal and idler fields, as opposed to entanglement involving vacuum states, is emphasized. We discuss the fundamental limitations of a theory in which these vacuum fields are treated as classical, stochastic fields.

]]>Atoms doi: 10.3390/atoms7010026

Authors: Edi Bon Paola Marziani Predrag Jovanović Nataša Bon

The mechanism of the optical variability of active galactic nuclei (AGN) is still very puzzling. It is now widely accepted that the optical variability of AGN is stochastic, producing red noise-like light curves. In case they were to be periodic or quasi-periodic, one should expect that the time scales of optical AGN variability should relate to orbiting time scales of regions inside the accretion disks with temperatures mainly emitting the light in this wavelength range. Knowing the reverberation scales and masses of AGN, expected orbiting time scales are in the order of decades. Unfortunately, most of monitored AGN light curves are not long enough to investigate such time scales of periodicity. Here we investigate the AGN optical variability time scales and their possible connections with the broad emission line shapes.

]]>Atoms doi: 10.3390/atoms7010025

Authors: Eugene Oks

The development of various spectroscopic diagnostics of relatively weak Langmuir waves in plasmas and their successful implementation have a history of over 50 years. As for spectroscopic diagnostics of Langmuir solitons (i.e., relatively strong Langmuir waves) in plasmas, there have only been very few theoretical papers. The most promising result so far was based on using satellites of the dipole-forbidden spectral lines of He, Li, or He-like and Li-like ions. It was shown that, in the case of Langmuir solitons, the peak intensity of the satellites of the dipole-forbidden lines can be significantly enhanced&mdash;by orders of magnitude&mdash;compared to the case of non-solitonic Langmuir waves. This distinctive feature of satellites under Langmuir solitons allows them to be distinguished from non-solitonic Langmuir waves. In the present paper, we perform a general study of the effects of Langmuir solitons on arbitrary spectral lines of hydrogen or hydrogen-like ions. Then, using the Ly-beta line as an example, we compare the main features of the profiles for the case of the Langmuir solitons with the case of the non-solitonic Langmuir waves of the same amplitude. We also show how the line profiles depend on the amplitude of the Langmuir solitons and on their separation from each other within the sequence of the solitons.

]]>Atoms doi: 10.3390/atoms7010024

Authors: Mioljub Nesic Marica Popovic Slobodanka Galovic

In this work, theoretically/mathematically simulated models are derived for the photoacoustic (PA) frequency response of both volume and surface optically-absorbing samples in a minimum volume PA cell. In the derivation process, the thermal memory influence of both the sample and the air of the gas column are accounted for, as well as the influence of the measurement chain. Within the analysis of the TMS model, the influence of optical, thermal, and elastic properties of the sample was investigated. This analysis revealed that some of the processes, characterized by certain sample properties, exert their dominance only in limited modulation frequency ranges, which are shown to be dependent upon the choice of the sample material and its thickness. Based on the described analysis, two methods are developed for TMS model parameter determination, i.e., sample properties which dominantly influence the PA response in the measurement range: a self-consistent procedure for solving the exponential problems of mathematical physics, and a well-trained three-layer perceptron with back propagation, based upon theory of neural networks. The results of the application of both inverse problem solving methods are compared and discussed. The first method is shown to have the advantage in the number of properties which are determined, while the second one is advantageous in gaining high accuracy in the determination of thermal diffusivity, explicitly. Finally, the execution of inverse PA problem is implemented on experimental measurements performed on macromolecule samples, the results are discussed, and the most important conclusions are derived and presented.

]]>Atoms doi: 10.3390/atoms7010023

Authors: Mohammed Koubiti Roshin Raj Sheeba

Modeling of the spectral line and continuum radiation emitted by hydrogen isotopes in peripheral regions of magnetic fusion is presented through profiles of the Zeeman-Doppler broadened H&alpha;/D&alpha; line and those of the Stark broadened high-n Balmer lines extending beyond the series limit for recombining plasmas. The H&alpha;/D&alpha; line profiles should be modelled while accounting for several populations of neutrals to mimic real situations and analyze experimental data for isotopic ratio determination. On the other side, high-n Balmer lines of hydrogen are used for plasma electron density and temperature diagnostics. Moreover, modelling whole spectra including the continuum radiation contributes to the development of synthetic diagnostics for future magnetic fusion devices for which they can give predictive results through coupling to numerical simulation tools.

]]>Atoms doi: 10.3390/atoms7010022

Authors: Milan S. Dimitrijević Vladimir A. Srećković Alaa Abo Zalam Nikolai N. Bezuglov Andrey N. Klyucharev

Atoms and molecules in highly excited (Rydberg) states have a number of unique characteristics due to the strong dependence of their properties on the values of principal quantum numbers. The paper discusses the results of an investigation of collisional Rydberg complexes specific features, resulting in the development of dynamic chaos and the accompanying diffusion autoionization processes. It is shown (experiment and theory) that, in subthermal low energies, the global chaotic regime that evolved in quasimolecular systems leads to significant changes in the Rydberg gases radiation/ionization kinetics. The effect of F&ouml;rster resonance on the width of the fluorescence spectra and stochastic ionization processes in Rydberg systems is also discussed.

]]>Atoms doi: 10.3390/atoms7010021

Authors: Nazeran Idrees Muhammad Jawwad Saif Tehmina Anwar

Topological index is an invariant of molecular graphs which correlates the structure with different physical and chemical invariants of the compound like boiling point, chemical reactivity, stability, Kovat&rsquo;s constant etc. Eccentricity-based topological indices, like eccentric connectivity index, connective eccentric index, first Zagreb eccentricity index, and second Zagreb eccentricity index were analyzed and computed for families of Dutch windmill graphs and circulant graphs.

]]>Atoms doi: 10.3390/atoms7010020

Authors: Stambulchik Calisti Chung González

The Spectral Line Shapes in Plasmas (SLSP) code comparison workshop series [...]

]]>Atoms doi: 10.3390/atoms7010019

Authors: Victor E. Colussi

The two- and three-body contacts are central to a set of univeral relations between microscopic few-body physics within an ultracold Bose gas and its thermodynamical properties. They may also be defined in trapped few-particle systems, which is the subject of this work. In this work, we focus on the unitary three-body problem in a trap, where interactions are as strong as allowed by quantum mechanics. We derive analytic results for the two- and three-body contacts in this regime and compare them with existing limiting expressions and previous numerical studies.

]]>Atoms doi: 10.3390/atoms7010018

Authors: Paola Marziani Edi Bon Natasa Bon Ascension del Olmo Mary Loli Martínez-Aldama Mauro D’Onofrio Deborah Dultzin C. Alenka Negrete Giovanna M. Stirpe

Quasars accreting matter at very high rates (known as extreme Population A (xA) or super-Eddington accreting massive black holes) provide a new class of distance indicators covering cosmic epochs from the present-day Universe up to less than 1 Gyr from the Big Bang. The very high accretion rate makes it possible that massive black holes hosted in xA quasars can radiate at a stable, extreme luminosity-to-mass ratio. This in turn translates into stable physical and dynamical conditions of the mildly ionized gas in the quasar low-ionization line emitting region. In this contribution, we analyze the main optical and UV spectral properties of extreme Population A quasars that make them easily identifiable in large spectroscopic surveys at low- ( z ≲ 1 ) and intermediate-z (2 ≲ z ≲ 2.6), and the physical conditions that are derived for the formation of their emission lines. Ultimately, the analysis supports the possibility of identifying a virial broadening estimator from low-ionization line widths, and the conceptual validity of the redshift-independent luminosity estimates based on virial broadening for a known luminosity-to-mass ratio.

]]>Atoms doi: 10.3390/atoms7010017

Authors: Dennis Bodewits Ronnie Hoekstra

Absolute Extreme Ultraviolet emission cross-sections have been measured for collisions between C 5 + and H 2O in the range of 0.113 to 3.75 keV/amu (170&ndash;979 km/s). These results are used to derive velocity-dependent triplet-to-singlet ratios and emission cross-sections of the Cv K-series following single-electron capture. Comparison with existing measurements of integral charge-changing cross-sections indicates that auto-ionizing multi-electron capture is a significant reactions channel. This reaction may indirectly populate the n = 2 states and thus add strength to the K &alpha; emission of Cv ions thereby co-determining the hardness ratio of K-series emission of Cv.

]]>Atoms doi: 10.3390/atoms7010016

Authors: Marko Ćosić Srđan Petrović Nebojša Nešković

Here we report the results of the theoretical investigation of the transmission of channeled positrons through various short chiral single walled carbon nanotubes (SWCNT). The main question answered by this study is &ldquo;What are the manifestations of the rainbow effect in the channeling of quantum particles that happens during the channeling of classical particles?&rdquo; To answer this question, the corresponding classical and quantum problems were solved in parallel, critically examined, and compared with each other. Positron energies were taken to be 1 MeV when the quantum approach was necessary. The continuum positron-nanotube potential was constructed from the thermally averaged Moli&egrave;re&rsquo;s positron-carbon potential. In the classical approach, a positron beam is considered as an ensemble of noninteracting particles. In the quantum approach, it is considered as an ensemble of noninteracting wave packages. Distributions of transmitted positrons were constructed from the numerical solutions of Newton&rsquo;s equation and the time-dependent Schr&ouml;dinger equation. For the transmission of 1-MeV positrons through 200-nm long SWCNT (14; 4), in addition to the central maximum, the quantum angular distribution has a prominent peak pair (close to the classical rainbows) and two smaller peaks pairs. We have shown that even though the semiclassical approximation is not strictly applicable it is useful for explanation of the observed behavior. In vicinity of the most prominent peak, i.e., the primary rainbow peak, rays interfere constructively. On one of its sides, rays become complex, which explains the exponential decay of the probability density in that region. On the other side, the ray interference alternates between constructive and destructive, thus generating two observed supernumerary rainbow peaks. The developed model was then applied for the explanation of the angular distributions of 1-MeV positrons transmitting through 200 nm long (7, 3), (8, 5), (9, 7), (14, 4), (16, 5) and (17, 7) SWCNTs. It has been shown that this explains most but not all rainbow patterns. Therefore, a new method for the identification and classification of quantum rainbows was developed relying only on the morphological properties of the positron wave function amplitude and the phase function families. This led to a detailed explanation of the way the quantum rainbows are generated. All wave packets wrinkle due to their internal focusing in a mutually coordinated way and are concentrated near the position of the corresponding classical rainbow. This explanation is general and applicable to the investigations of quantum effects occurring in various other atomic collision processes.

]]>Atoms doi: 10.3390/atoms7010015

Authors: Anthony C. K. Leung Tom Kirchner

The Ne8+&ndash;He and &ndash;H2 collision systems are examined at impact speeds ranging between 0.17 and 0.4 a.u. Transition probabilities for electron capture are obtained using the two-center basis generator method performed within the independent-electron model. The aim of calculating capture cross sections for these collision systems is to provide new theoretical verification of previously reported experimental data and to provide aid for astrophysical X-ray studies. This study also examines the applicability of the independent-electron model with effective potentials to describe two-electron capture for these two systems. Comparisons of capture cross sections and radiative-emission counts with the available experimental and theoretical data show an overall good agreement.

]]>Atoms doi: 10.3390/atoms7010014

Authors: Andrei V. Pipa Ronny Brandenburg

Measurements of current and voltage are the basic diagnostics for electrical discharges. However, in the case of dielectric barrier discharges (DBDs), the measured current and voltage waveforms are influenced by the discharge reactor geometry, and thus, interpretation of measured quantities is required to determine the discharge properties. This contribution presents the main stages of the development of electrical diagnostics of DBDs, which are based on lumped electrical elements. The compilation and revision of the contributions to the equivalent circuit approach are targeted to indicate: (1) the interconnection between the stage of development, (2) its applicability, and (3) the current state-of-the-art of this approach.

]]>Atoms doi: 10.3390/atoms7010013

Authors: Nikolay A. Dyatko Yury Z. Ionikh Anatoly P. Napartovich

The present paper is based on the materials of the Invited Lecture presented at 29th Summer School and International Symposium on the Physics of Ionized Gases (28 August 2018&ndash;1 September 2018, Belgrade, Serbia). In the paper, the effect of nitrogen admixture on various characteristics of a dc glow discharge in argon (the volt-ampere characteristic, rate of plasma decay in the afterglow, discharge constriction condition, and formation of a partially constricted discharge) is considered.

]]>Atoms doi: 10.3390/atoms7010012

Authors: Milos Vlainic Ondrej Ficker Jan Mlynar Eva Macusova the COMPASS Tokamak Team

Runaway electrons present a potential threat to the safe operation of future nuclear fusion large facilities based on the tokamak principle (e.g., ITER). The article presents an implementation of runaway electron current estimations at COMPASS tokamak. The method uses a theoretical method developed by Fujita et al., with the difference in using experimental measurements from EFIT and Thomson scattering. The procedure was explained on the COMPASS discharge number 7298, which has a significant runaway electron population. Here, it was found that at least 4 kA of the plasma current is driven by the runaway electrons. Next, the method aws used on the set of plasma discharges with the variable electron plasma density. The difference in the plasma current was explained by runaway electrons, and their current was estimated using the aforementioned method. The experimental results are compared with the theory and simulation. The comparison presented some disagreements, showing the possible direction for the code development. Additional application on runaway electron energy limit is also addressed.

]]>Atoms doi: 10.3390/atoms7010011

Authors: Bratislav P. Marinković Vladimir A. Srećković Veljko Vujčić Stefan Ivanović Nebojša Uskoković Milutin Nešić Ljubinko M. Ignjatović Darko Jevremović Milan S. Dimitrijević Nigel J. Mason

In this contribution we present a progress report on two atomic and molecular databases, BEAMDB and MolD, which are web services at the Serbian virtual observatory (SerVO) and nodes within the Virtual Atomic and Molecular Data Center (VAMDC). The Belgrade Electron/Atom (Molecule) DataBase (BEAMDB) provides collisional data for electron interactions with atoms and molecules. The Photodissociation (MolD) database contains photo-dissociation cross sections for individual rovibrational states of diatomic molecular ions and rate coefficients for the chemi-ionisation/recombination processes. We also present a progress report on the major upgrade of these databases and plans for the future. As an example of how the data from the BEAMDB may be used, a review of electron scattering from methane is described.

]]>Atoms doi: 10.3390/atoms7010010

Authors: Milan S. Dimitrijević

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

]]>Atoms doi: 10.3390/atoms7010009

Authors: Nikola V. Ivanović

The cathode sheath (CS) region is the most important part of abnormal glow discharge (GD), where various processes relevant for the operation and application occur. The most important parameter of the CS is the distribution of electric field strength E which is of crucial importance for charged particles acceleration, their trajectories, kinetic energies, and collisions with other particles and cathode sputtering. All these processes are relevant for the operation of GD as well as for numerous applications in the field of spectroscopic analysis, plasma etching, thin film deposition, and depth profiling of cathode material. Thus, the importance of non-perturbing technique for E distribution measurement in the CS region was recognized long time ago. Within this article, a simple technique based on standard optical emission spectroscopy (OES) and typical laboratory equipment has been used for E mapping in the CS region of an abnormal glow discharge.

]]>Atoms doi: 10.3390/atoms7010008

Authors: Lazar Gavanski

The analysis of experimental Stark halfwidths of spectral lines of singly ionized oxygen and silicon and double ionized silicon is presented in this work. The considered spectral lines were emitted from plasma generated in an electromagnetically driven T-tube, with an electron temperature of 15,000 K and electron density of 1.45 &times; 1023 m&minus;3. The obtained Stark halfwidths were compared to experimental values given by other authors. In addition, all experimental values were compared to theoretical values. These data are useful for diagnostics of laboratory and astrophysical plasmas as well as verifying theoretical models.

]]>Atoms doi: 10.3390/atoms7010007

Authors: Atoms Editorial Office

Rigorous peer-review is the corner-stone of high-quality academic publishing [...]

]]>Atoms doi: 10.3390/atoms7010006

Authors: Maja S. Rabasovic Mihailo D. Rabasovic Bratislav P. Marinkovic Dragutin Sevic

We describe a streak camera system that is capable of both spatial and spectral measurements of laser-induced plasma. The system is based on a Hamamatsu C4334 streak camera and SpectraPro 2300i spectrograph. To improve the analysis of laser-induced plasma development, it is necessary to determine the timing of laser excitation in regard to the time scale on streak images. We present several methods to determine the laser signal timing on streak images&mdash;one uses the fast photodiode, and other techniques are based on the inclusion of the laser pulse directly on the streak image. A Nd:YAG laser (&lambda; = 1064 nm, Quantel, Brilliant B) was employed as the excitation source. The problem of synchronization of the streak camera with the Q-switched Nd:YAG laser is also analyzed. A simple modification of the spectrograph enables easy switching between the spectral and spatial measurement modes.

]]>Atoms doi: 10.3390/atoms7010005

Authors: Arnaud Bultel Vincent Morel Julien Annaloro

In this paper, we analyze the departure from equilibrium in two specific types of thermal plasmas. The first type deals with the plasma produced during the atmospheric entry of a spatial vehicle in the upper layers of an atmosphere, specifically the one of Mars. The second type concerns the plasma produced during the laser-matter interaction above the breakdown threshold on a metallic sample. We successively describe the situation and give the way along which modeling tools are elaborated by avoiding any assumption on the thermochemical equilibrium. The key of the approach is to consider the excited states of the different species as independent species. Therefore, they obey to conservation equations involving collisional-radiative contributions related to the other excited states. These contributions are in part due to the influence of electrons and heavy particles having a different translation temperature. This &lsquo;state-to-state&rsquo; approach then enables the verification of the excitation equilibrium by analyzing Boltzmann plots. This approach leads finally to a thorough analysis of the progressive coupling until the equilibrium asymptotically observed.

]]>Atoms doi: 10.3390/atoms7010004

Authors: Vesna Borka Jovanović Predrag Jovanović Duško Borka Salvatore Capozziello

The global properties of elliptical galaxies are connected through the so-called fundamental plane of ellipticals, which is an empirical relation between their parameters: effective radius, central velocity dispersion and mean surface brightness within the effective radius. We investigated the relation between the parameters of the fundamental plane equation and the parameters of modified gravity potential f ( R ) . With that aim, we compared theoretical predictions for circular velocity in f ( R ) gravity with the corresponding values from a large sample of observed elliptical galaxies. Besides, we consistently reproduced the values of coefficients of the fundamental plane equation as deduced from observations, showing that the photometric quantities like mean surface brightness are related to gravitational parameters. We show that this type of modified gravity, especially its power-law version— R n , is able to reproduce the stellar dynamics in elliptical galaxies. In addition, it is shown that R n gravity fits the observations very well, without the need for a dark matter.

]]>Atoms doi: 10.3390/atoms7010003

Authors: Vladimir A. Srećković Milan S. Dimitrijević Nikolai N. Bezuglov

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

]]>Atoms doi: 10.3390/atoms7010002

Authors: Anand K. Bhatia

Lyman-&alpha; radiation ( 2 P &rarr; 1 S ) has been seen from astrophysical sources and the sun. The line shape of this transition has been measured recently in Ps atoms both inside and outside a porous silica target. In the photodetachment of Ps&minus;, the residual Ps atom can be left in the 2P state instead of the 1S state giving rise to positronium Lyman radiation at 2432 A0. Photodetachment cross sections of Ps&minus; have been calculated when the Ps atom is left in nP states, n being 2, 3, 4, 5, 6 and 7, using the asymptotic form of the bound-state wave function and a plane wave for the final state wave function, following the approach of Ohmura and Ohmura [Phys. Rev. 1960, 118, 154] in the photodetachment of H&minus;.

]]>Atoms doi: 10.3390/atoms7010001

Authors: Ryan Carollo Alexander Frenett David Hanneke

Vibrational overtones in deeply-bound molecules are sensitive probes for variation of the proton-to-electron mass ratio μ . In nonpolar molecules, these overtones may be driven as two-photon transitions. Here, we present procedures for experiments with 16 O 2 + , including state-preparation through photoionization, a two-photon probe, and detection. We calculate transition dipole moments between all X 2 Π g vibrational levels and those of the A 2 Π u excited electronic state. Using these dipole moments, we calculate two-photon transition rates and AC-Stark-shift systematics for the overtones. We estimate other systematic effects and statistical precision. Two-photon vibrational transitions in 16 O 2 + provide multiple routes to improved searches for μ variation.

]]>Atoms doi: 10.3390/atoms6040070

Authors: F. E. Wietfeldt

Free neutron decay is a fundamental process in particle and nuclear physics. It is the prototype for nuclear beta decay and other semileptonic weak particle decays. Neutron decay played a key role in the formation of light elements in the early universe. The precise value of the neutron mean lifetime, about 15 min, has been the subject of many experiments over the past 70 years. The two main experimental methods, the beam method and the ultracold neutron storage method, give average values of the neutron lifetime that currently differ by 8.7 s (4 standard deviations), a serious discrepancy. The physics of neutron decay, implications of the neutron lifetime, previous and recent experimental measurements, and prospects for the future are reviewed.

]]>Atoms doi: 10.3390/atoms6040069

Authors: Yasuhiko Takeiri

The Large Helical Device (LHD) is one of the world&rsquo;s largest superconducting helical system fusion-experiment devices. Since the start of experiments in 1998, it has expanded its parameter regime. It has also demonstrated world-leading steady-state operation. Based on this progress, the LHD has moved on to the advanced research phase, that is, deuterium experiment, which started in March 2017. During the first deuterium experiment campaign, an ion temperature of 10 keV was achieved. This was a milestone in helical systems research: demonstrating one of the conditions for fusion. All of this progress and increased understanding have provided the basis for designing an LHD-type steady-state helical fusion reactor. Moreover, LHD plasmas have been utilized not only for fusion research, but also for diagnostics development and applications in wide-ranging plasma research. A few examples of such contributions of LHD plasmas (spectroscopic study and the development of a new type of interferometer) are introduced in this paper.

]]>Atoms doi: 10.3390/atoms6040068

Authors: François Frémont

A four-body classical model based on the resolution of Hamilton equations of motion was used here to determine and analyze ionization doubly-differential cross sections following 3.6 MeV/amu Au53+ + He collisions. Our calculation was not able to reproduce the binary peaks experimentally observed in the transverse momentum distributions for electron emission energies larger than 10 eV. Surprisingly, by introducing a large number of free or quasi-free electrons that followed the projectile at the same velocity, the agreement between the experiment and our calculation was improved, since our model reproduced, at least qualitatively, the experimental binary peaks. The origin of the presence of such electrons is discussed.

]]>Atoms doi: 10.3390/atoms6040067

Authors: Robert Beuc Mladen Movre Goran Pichler

In the paper, several theoretical approaches to the determination of the reduced absorption and emission coefficients under local thermodynamic equilibrium conditions were exposed and discussed. The full quantum-mechanical procedure based on the Fourier grid Hamiltonian method was numerically robust but time consuming. In that method, all transitions between the bound, free, and quasi-bound states were treated as bound&ndash;bound transitions. The semi-classical method assumed continuous energies of ro-vibrational states, so it did not give the ro-vibrational structure of the molecular bands. That approach neglected the effects of turning points but agreed with the averaged-out quantum-mechanical spectra and it was computer time efficient. In the semi-quantum approximation, summing over the rotational quantum number J was done analytically using the classical Franck&ndash;Condon principle and the stationary&ndash;phase approximation and its consumption of computer time was lower by a few orders of magnitude than the case of the full quantum-mechanical approach. The approximation described well the vibrational but not the rotational structure of the molecular bands. All the above methods were compared and discussed in the case of a visible and near infrared spectrum of LiHe, Li2, and Cs2 molecules in the high temperature range.

]]>Atoms doi: 10.3390/atoms6040066

Authors: Emmanouil P. Benis Ioannis Madesis Angelos Laoutaris Stefanos Nanos Theo J. M. Zouros

The use of mixed-state ionic beams in collision dynamics investigations is examined. Using high resolution Auger projectile spectroscopy involving He-like ( 1 s 2 1 S , 1 s 2 s 3 , 1 S ) mixed-state beams, the spectrum contributions of the 1 s 2 s 3 S metastable beam component is effectively separated and clearly identified. This is performed with a technique that exploits two independent spectrum measurements under the same collision conditions, but with ions having quite different metastable fractions, judiciously selected by varying the ion beam charge-stripping conditions. Details of the technique are presented together with characteristic examples. In collisions of 4 MeV B 3 + with H 2 targets, the Auger electron spectrum of the separated 1 s 2 s 3 S boron beam component allows for a detailed analysis of the formation of the 1 s 2 s ( 3 S ) n l 2 L states by direct n l transfer. In addition, the production of hollow 2 s 2 p 1 , 3 P doubly- and 2 s 2 p 2 2 D triply-excited states, by direct excitation and transfer-excitation processes, respectively, can also be independently studied. In similar mixed-state beam collisions of 15 MeV C 4 + with H 2 , He, Ne and Ar targets, the contributions of the 1 s 2 , 1 s 2 s 3 , 1 S beam components to the formation of the 2 s 2 p 3 , 1 P states by double-excitation, 1 s &rarr; 2 p excitation and transfer-loss processes can be clearly identified, facilitating comparisons with theoretical calculations.

]]>Atoms doi: 10.3390/atoms6040065

Authors: Andrea Proto Jon Tomas Gudmundsson

The one-dimensional object-oriented particle-in-cell Monte Carlo collision code oopd1 is applied to explore the role of secondary electron emission and electron reflection on the properties of the capacitively-coupled oxygen discharge. At low pressure (10 mTorr), drift-ambipolar heating of the electrons dominates within the plasma bulk, while at higher pressure (50 mTorr), stochastic electron heating in the sheath region dominates. Electron reflection has negligible influence on the electron energy probability function and only a slight influence on the electron heating profile and electron density. Including ion-induced secondary electron emission in the discharge model introduces a high energy tail to the electron energy probability function, enhances the electron density, lowers the electronegativity, and increases the effective electron temperature in the plasma bulk.

]]>Atoms doi: 10.3390/atoms6040064

Authors: María Silvia Gravielle Jorge Esteban Miraglia Leandro Frisco

Coherence properties of projectiles, found relevant in ion-atom collisions, are investigated by analyzing the influence of the degree of coherence of the atomic beam on interference patterns produced by grazing-incidence fast-atom diffraction (GIFAD or FAD). The transverse coherence length of the projectiles, which depends on the incidence conditions and the collimating setup, determines the overall characteristics of GIFAD distributions. We show that for atoms scattered from a LiF(001) surface after a given collimation, we can modify the interference signatures of the angular spectra by varying the total impact energy, while keeping the normal energy as a constant. Also, the role played by the geometry of the collimating aperture is analyzed, comparing results for square and circular openings. Furthermore, we study the spot-beam effect, which is due to different focus points of the impinging particles. We show that when a region narrower than a single crystallographic channel is coherently illuminated by the atomic beam, the spot-beam contribution strongly affects the visibility of the interference structures, contributing to the gradual quantum-classical transition of the projectile distributions.

]]>Atoms doi: 10.3390/atoms6040063

Authors: Jonas R. Persson

The hyperfine anomalies in Gd and Nd have been extracted from experimental hyperfine structure constants. In addition to the values of the hyperfine anomaly, new improved values of the nuclear magnetic dipole moment ratios are derived.

]]>Atoms doi: 10.3390/atoms6040062

Authors: Hong Yang Muhammad Kamran Siddiqui Misbah Arshad Muhammad Naeem

Chemical graph theory comprehends the basic properties of an atomic graph. The sub-atomic diagrams are the graphs that are comprised of particles called vertices and the covalent bond between them are called edges. The eccentricity ϵ u of vertex u in an associated graph G, is the separation among u and a vertex farthermost from u. In this article, we consider the precious stone structure of cubic carbon and registered Eccentric-connectivity index &xi; ( G ) , Eccentric connectivity polynomial E C P ( G , x ) and Connective Eccentric index C &xi; ( G ) of gem structure of cubic carbon for n-levels.

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