Search

We report recent enhancements to the online atomic database at the Ohio State University, NORAD-Atomic-Data, that provide various parameters for radiative and collisional atomic processes dominant in astrophysical plasma. NORAD stands for Nahar Osu RADiative. The database belongs to the data sources, especially for the latest works, of the international collaborations of the Opacity Project and the Iron Project. The contents of the database are calculated values for energies, oscillator strengths, radiative decay rates, lifetimes, cross-sections for photoionization, electron-ion recombination cross-sections, and recombination rate coefficients. We have recently expanded NORAD-Atomic-Data with several enhancements over those reported earlier. They are as follows: (i) We continue to add energy levels, transition parameters, cross-sections, and recombination rates for atoms and ions with their publications. (ii) Recently added radiative atomic data contain a significant amount of transition data for photo-absorption spectral features corresponding to the X-ray resonance fluorescence effect, showing prominent wavelength regions of bio-signature elements, such as phosphorus ions, and emission bumps of heavy elements, such as of lanthanides, which may be created in a kilonova event. We are including (iii) collisional data for electron-impact-excitation, (iv) experimental data for energies and oscillator strengths for line formation, (v) experimental cross-sections for photoionization that can be applied for benchmarking and other applications, and (vi) the introduction of a web-based interactive feature to calculate spectral line ratios at various plasma temperature and density diagnostics, starting with our recently published data for P II. We presented a summary description of theoretical backgrounds for the computed data in the earlier paper. With the introduction of experimental results in the new version of NORAD, we present a summary description of measurement of high-resolution photoionization cross-sections at an Advanced Light Source of LBNL synchrotron set-up and briefly discuss other set-ups. These additions should make NORAD-Atomic-Data more versatile for various applications. For brevity, we provide information on the extensions and avoid repetition of data description of the original paper. [ABSTRACT FROM AUTHOR]

We report recent enhancements to the online atomic database at the Ohio State University, NORAD-Atomic-Data, that provide various parameters for radiative and collisional atomic processes dominant in astrophysical plasma. NORAD stands for Nahar Osu RADiative. The database belongs to the data sources, especially for the latest works, of the international collaborations of the Opacity Project and the Iron Project. The contents of the database are calculated values for energies, oscillator strengths, radiative decay rates, lifetimes, cross-sections for photoionization, electron-ion recombination cross-sections, and recombination rate coefficients. We have recently expanded NORAD-Atomic-Data with several enhancements over those reported earlier. They are as follows: (i) We continue to add energy levels, transition parameters, cross-sections, and recombination rates for atoms and ions with their publications. (ii) Recently added radiative atomic data contain a significant amount of transition data for photo-absorption spectral features corresponding to the X-ray resonance fluorescence effect, showing prominent wavelength regions of bio-signature elements, such as phosphorus ions, and emission bumps of heavy elements, such as of lanthanides, which may be created in a kilonova event. We are including (iii) collisional data for electron-impact-excitation, (iv) experimental data for energies and oscillator strengths for line formation, (v) experimental cross-sections for photoionization that can be applied for benchmarking and other applications, and (vi) the introduction of a web-based interactive feature to calculate spectral line ratios at various plasma temperature and density diagnostics, starting with our recently published data for P II. We presented a summary description of theoretical backgrounds for the computed data in the earlier paper. With the introduction of experimental results in the new version of NORAD, we present a summary description of measurement of high-resolution photoionization cross-sections at an Advanced Light Source of LBNL synchrotron set-up and briefly discuss other set-ups. These additions should make NORAD-Atomic-Data more versatile for various applications. For brevity, we provide information on the extensions and avoid repetition of data description of the original paper.

The results of experimental and theoretical studies on electron-impact excitation of the 6 s 6 p   P 1 °   3 → 6 s 2   S 0   1 (λ190.8 nm) and 6 s 7 s   S 0   1 → 6 s 6 p   P 1 °   3 (λ179.9 nm) intercombination transitions in the single-charged thallium ion are presented. The crossed-beams technique was used in combination with a spectroscopic method in the experiment. A distinct structure revealed in the cross-sections of both lines results from electron decay of atomic autoionizing states and radiative transitions from upper ionic levels. The dominant mechanism of the structure formation was the Coster–Kronig process. Relativistic distorted wave calculations were performed to obtain emission cross-sections for the above transitions. The absolute values of the cross-sections were found to be (0.25 ± 0.08) × 10−16 cm2 (λ190.8 nm) and (0.10 ± 0.04) × 10−16 cm2 (λ179.9 nm) at the electron energy of 100 eV. [ABSTRACT FROM AUTHOR]

The excitation cross sections of the 2P state of atomic hydrogen at low incident electron energies (from 0.755 to 3.5 Ry) were calculated using the variational polarized orbital method. Up to 13 partial waves (L = 1, 13) were used to obtain converged cross sections in the above energy range. The importance of the long-range forces is pointed out in the threshold region, and behavior of the cross section is indicated near the threshold. The polarization P of radiation emitted at right angle to the incident electron beam was calculated and the perpendicular cross section was also calculated. [ABSTRACT FROM AUTHOR]

Results of experimental and theoretical investigations into the electron-impact excitation of the resonance 6 s 6 p 1 P 1 ° â†' 6 s 21 S 0 (132.2 nm), as well as the cascade 6 s 7 s 1 S 0 â†' 6 s 6 p 1 P 1 ° (309.2 nm) and 6 p 21 D 2 â†' 6 s 6 p 1 P 1 ° (150.8 nm) spectral transitions from the ground 6 s 21 S 0 level in the thallium ion, are presented. Crossed beams of electrons and Tl+ ions in combination with a spectroscopic method were used in the experiment. Measured cross sections have a distinct resonance structure arising mainly from the electron decay of atomic 5 d 96 s 26 p 2, 5 d 106 s 7 s (1 S) np (n â©ľ 7), 5 d 106 s 6 d (1 D) np (n â©ľ 6), 5 d 106 s 6 d (1 D) nd (n â©ľ 6) and ionic 5 d 96 s 2 np, 5 d 96 s 2 nd, 5 d 96 snp (n â©ľ 6) autoionizing levels, as well as radiative transitions from the higher 6 s 7 s 1 S 0, 6 s 6 d 1 D 2, and 6 p 21 D 2, 1 S 0 ionic levels. Relativistic distorted wave (RDW) calculations are performed to obtain the effective cross sections for the above transitions. The absolute values of the cross sections are found to be 1.39 Ă— 10âˆ'16 cm2 at 300 eV for the λ 132.2 nm resonance line, and 0.11 Ă— 10âˆ'16 cm2 and 0.56 Ă— 10âˆ'16 cm2 at 100 eV for the λ 309.2 nm and λ 150.8 nm lines, respectively. The contribution of the cascade transitions being studied to the effective cross section of the λ 132.2 nm resonance line at the energy of 100 eV is about 30%. A calculation using the semi-empirical Van Regemorter formula is also performed to obtain the effective cross section of the resonance λ 132.2 nm line. The absolute value of the cross section at 300 eV is found to be nearly the same as that given by the RDW calculation. [ABSTRACT FROM AUTHOR]

A most general density-matrix formalism is presented to investigate linear polarization of characteristic lines following electron-impact excitation of atoms or ions with arbitrary nuclear spin, which can account for depolarization of energy levels and multipole mixing of radiation fields. It is then applied to the linear polarization of the $K\alpha_{1}$ line radiated from heliumlike ions with nuclear spin $I \! = \! 1/2$ . As an example, detailed calculations are performed for $^{207}_{81}$ Tl ^79+ ions using the multi-configurational Dirac-Fock method and relativistic distorted-wave theory. It is found that the effect of the hyperfine interaction on the linear polarization depends dominantly on impact electron energy. For low impact energies close to the excitation threshold, the hyperfine interaction results in an enhancement of the linear polarization, especially for those photons emitted perpendicularly to the impact electron beam. In contrast, such a hyperfine-induced effect diminishes quickly with increasing impact energy and vanishes at medium and high energies, which is very different from the results for the case of radiative electron capture (Surzhykov et al 2013 Phys. Rev. A 87 052507). The present study is experimentally accessible at both electron-beam ion traps and ion storage rings and, thus, accurate $K\alpha_{1}$ polarization measurements at low energies can be utilized to probe the hyperfine interaction in highly charged few-electron ions.

The results of experimental and theoretical studies on electron-impact excitation of the 6s6p P1° 3→6s2 S0 1 (λ190.8 nm) and 6s7s S0 1→6s6p P1° 3 (λ179.9 nm) intercombination transitions in the single-charged thallium ion are presented. The crossed-beams technique was used in combination with a spectroscopic method in the experiment. A distinct structure revealed in the cross-sections of both lines results from electron decay of atomic autoionizing states and radiative transitions from upper ionic levels. The dominant mechanism of the structure formation was the Coster–Kronig process. Relativistic distorted wave calculations were performed to obtain emission cross-sections for the above transitions. The absolute values of the cross-sections were found to be (0.25 ± 0.08) × 10−16 cm2 (λ190.8 nm) and (0.10 ± 0.04) × 10−16 cm2 (λ179.9 nm) at the electron energy of 100 eV.

The excitation cross sections of the 2P state of atomic hydrogen at low incident electron energies (from 0.755 to 3.5 Ry) were calculated using the variational polarized orbital method. Up to 13 partial waves (L = 1, 13) were used to obtain converged cross sections in the above energy range. The importance of the long-range forces is pointed out in the threshold region, and behavior of the cross section is indicated near the threshold. The polarization P of radiation emitted at right angle to the incident electron beam was calculated and the perpendicular cross section was also calculated.

Electron-impact excitation of tungsten ions W q + (q = 4 0 − 4 3) has been studied using the fully relativistic distorted wave (RDW) theory. The excitation cross-sections of selected electric dipole allowed transitions of these ions to be determined for the incident electron energies from the excitation threshold to 20 keV. Further, the calculated cross-section results are fitted with an analytical expression for direct applications in plasma modeling. In addition, using the density matrix theory, the linear polarization of the photons emitted from the excited tungsten ions when decay to their respective ground states is presented. [ABSTRACT FROM AUTHOR]

The linear polarization of magnetic-quadrupole emission lines 1 s 2 2 s 2 p 3 / 2 3 P 2 → 1 s 2 2 s 2 1 S 0 and 1 s 2 s 2 2 p 3 / 2 3 P 2 → 1 s 2 2 s 2 1 S 0 following electron-impact excitation of Be-like ions with nuclear spin I = 1 / 2 is studied by employing the density-matrix theory and the relativistic distorted-wave theory. To explore the effects of the hyperfine interaction, detailed calculations are performed for the polarization of the magnetic-quadrupole lines emitted from A Xe 50 + (A = 125, 127, and 129) and A Tl 77 + (A = 187, 205, and 207) ions with different nuclear magnetic dipole moments μ I at a series of impact electron energies. It is shown that the hyperfine interaction strongly lowers the polarization of the 1 s 2 2 s 2 p 3 / 2 3 P 2 → 1 S 0 line at all considered impact energies, while its effects behave less and less prominent with increasing impact energy for the 1 s 2 s 2 2 p 3 / 2 3 P 2 → 1 S 0 line. In addition, we also find that the polarization of the 1 s 2 2 s 2 p 3 / 2 3 P 2 → 1 S 0 line is much more sensitive to μ I than that of the 1 s 2 s 2 2 p 3 / 2 3 P 2 → 1 S 0 line. In particular, for the 1 s 2 2 s 2 p 3 / 2 3 P 2 → 1 S 0 line of spin-1/2 Xe 50 + ions, the differences in the polarization among the isotopes are significant. These findings indicate that precise polarization measurements of magnetic-quadrupole lines of Be-like ions are expected to be used for exploring the hyperfine interaction and even the nuclear magnetic dipole moment of nonzero-spin isotopes. • Effects of hyperfine interaction on the linear polarization of M2 lines following electron-impact excitation of Be-like ions with nuclear spin I = 1/2 are studied. • Linear polarization of the 1 s 2 2 s 2 p 3 / 2 3 P 2 → 1 S 0 line is much more sensitive to the nuclear magnetic dipole moment than that of the 1 s 2 s 2 2 p 3 / 2 3 P 2 → 1 S 0 line. • High precision polarization measurements of the 1 s 2 2 s 2 p 3 / 2 3 P 2 → 1 S 0 line are proposed to explore the hyperfine interaction and nuclear magnetic dipole moment. [ABSTRACT FROM AUTHOR]

Results of experimental and theoretical investigation of electron-impact excitation of the 6s26d D2→6s26p P2o spectral transitions from the ground 6s26p P21/2o level in the Pb+ ion are presented. The experimental excitation functions for the transitions, measured by a VUV spectroscopy method, using the crossed electron and ion beams technique, reveal a rather distinct resonance structure resulting mainly from the electron decay of both atomic and ionic autoionizing states. The absolute values of the emission cross-sections, obtained by normalizing the experimental data at the incident electron energy 100 eV by those calculated using the Flexible Atomic Code software package, were found to be (0.35 ± 0.17) × 10–16 cm2 for the 6s26d D23/2 → 6s26p P21/2o (λ143.4 nm) transition and (0.19 ± 0.09) × 10–16 cm2 for the 6s26d D25/2 → 6s26p P23/2o (λ182.2 nm) transition.

Highlights • In the present work we consider 33 transitions arising out of electron impact N-shell excitations of four tungsten ions (W40 + to W43 +) and report the calculations of cross-sections in the wide range of incident electron energies for the application to the plasma modeling. • The calculations of the electron impact excitation cross-sections are performed using fully relativistic distorted wave theory. • We represented the bound states of tungsten ions through multi-configuration Dirac-Fock wave functions and calculated using the relativistic GRASP2k program while for continuum projectile electron wave functions we solve Dirac equations numerically. • For the plasma modeling purposes, the analytic fittings to our all calculated fine structure excitation cross-sections are also provided. • The linear polarizations of the photon emissions from these excited states to the ground state are also reported. Abstract Study of electron impact excitation of W40+ (Se-like), W41+ (As-like), W42+ (Ge-like), and W43+ (Ga-like) ions using fully relativistic distorted wave theory has been presented. The excitation cross-sections of E1 and E2 allowed transitions of these ions are reported across the wide range of incident electron energies from excitation threshold to 20 keV. The obtained cross-sections of all the transitions of the four ions are fitted with an analytical expression for the applications in the plasma modelling. Further, using the magnetic sublevel cross-sections, the degree of linear polarization of the photon emissions from the electron impact excited anisotropic states of tungsten ions through the dipole allowed transitions are also calculated. [ABSTRACT FROM AUTHOR]

The online atomic database of NORAD-Atomic-Data, where NORAD stands for Nahar OSU Radiative, is part of the data sources of the two international collaborations of the Opacity Project (OP) and the Iron Project (IP). It contains large sets of parameters for the dominant atomic processes in astrophysical plasmas, such as, (i) photo-excitation, (ii) photoionization, (iii) electron–ion recombination, (iv) electron–impact excitations. The atomic parameters correspond to tables of energy levels, level-specific total photoionization cross-sections, partial photoionization cross-sections of all bound states for leaving the residual ion in the ground state, partial cross-sections of the ground state for leaving the ion in various excited states, total level-specific electron–ion recombination rate coefficients that include both the radiative and dielectronic recombination, total recombination rate coefficients summed from contributions of an infinite number of recombined states, total photo-recombination cross-sections and rates with respect to photoelectron energy, transition probabilities, lifetimes, collision strengths. The database was created after the first two atomic databases, TOPbase under the OP and TIPbase under the IP. Hence the contents of NORAD-Atomic-Data are either new or from repeated calculations using a much larger wave function expansion making the data more complete. The results have been obtained from the R-matrix method using the close-coupling approximation developed under the OP and IP, and from atomic structure calculations using the program SUPERSTRUCTURE. They have been compared with available published results which have been obtained theoretically and experimentally, and are expected to be of high accuracy in general. All computations were carried out using the computational facilities at the Ohio Supercomputer Center (OSC) starting in 1990. At present it contains atomic data for 154 atomic species, 98 of which are lighter atomic species with nuclear charge Z ≤ 28 and 56 are heavier ones with Z > 28. New data are added with publications.

Electron impact excitation of highly charged tungsten ions in the framework of a fully relativistic distorted wave approach is considered in this paper. Calculations of electron impact excitation cross-sections for the M- and L-shell transitions in the tungsten ions Wn+ (n = 44–66) and polarization of the decay of photons from the excited tungsten ions are briefly reviewed and discussed. New calculations in the wide range of incident electron energies are presented for M-shell transitions in the K-like through Ne-like tungsten ions.

The excitation cross sections of the 2S state of atomic hydrogen at 10 low incident electron energies (10.30 and 54.5 eV) have been calculated using the variational polarized method. Nine partial waves are used to get convergence of cross sections in the above energy range. The maximum of the cross section is 0.137 πa0² at 11.14 eV which is close to the experimental result 0.163 ± 0.2 πa0² at 11.6 ± 0.2 eV. The present results are compared with other calculations, many of them are based on the close-coupling approximation, including the R-matrix method. Differential cross sections at 13.6 eV incident energy have also been calculated. Spin-flip cross sections have been calculated and compared with those obtained using the close-coupling approximation. [ABSTRACT FROM AUTHOR]

Sulphur is one of the most abundant chemical elements in the universe and a large number of lines have been observed in the spectra of astrophysical object. The S IV and SV ions considered in this work have received much interest in the last decade. The main objective of the present work is to report on photoionization cross-sections of S IV using the Breit-Pauli R -matrix (BPRM) method. We have carried out extensive non-relativistic and relativistic calculations of the photoionization cross sections to focus on relativistic effects. The reliability of the atomic data presented here has been carefully tested. We have exploited the BPRM code to describe the atomic wavefunctions and generate the energy levels for the SV 81 fine-structure bound target states and the corresponding A -values for transitions between these levels. The partial and total cross sections for the photoionization of the Al-like S 3+ ground and excited states are determined for photon energy ranging from the S 4+ 3s 2 threshold up to the S 4+ 4s threshold. We present statistically weighted, level resolved ground photoionization cross sections for the S IV ion. Both resonance positions and the oscillator strengths are presented. Extensive comparison of the present calculated values with those obtained from direct theoretical scattering calculation is also presented. To the best of our knowledge, the work reported herein describes for the first time a detailed relativistic photoionization calculation for this system, and the results are relevant to the laboratory and astrophysical plasmas. [ABSTRACT FROM AUTHOR]

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.

Employing the independent-process and isolated-resonance approximations using distorted-waves (IPIRDW), we have performed a series of calculations of the resonance-enhanced electron-impact excitations (EIE) among 27 singly excited levels from the n ≤ 6 configurations of Cu-like gold (Au, Z = 79 ). Resonance excitation (RE) contributions from both the n = 4 → 4 − 7 and n = 3 → 4 core excitations have been considered. Our results demonstrate that RE contributions are significant and enhance the effective collision strengths (ϒ) of certain excitations by up to an order of magnitude at low temperature (10 6.1 K), and are still important at relatively high temperature (10 7.5 K). Results from test calculations of the resonance-enhanced EIE processes among 16 levels from the n ≤ 5 configurations using both the Dirac R -matrix (DRM) and IPIRDW approaches agree very well with each other. This means that the close-coupling effects are not important for this ion, and thus warrants the reliability of present resonance-enhanced EIE data among the 27 levels. The results from the collisional-radiative model (CRM) show that, at 3000 eV, near where Cu-like Au is most abundant, RE contributions have important effects (up to 25%) on the density diagnostic line intensity ratios, which are sensitive near 10 20 cm − 3 . The present work is the first EIE research including RE contributions for Cu-like Au. Our EIE data are more accurate than previous results due to our consideration of RE contributions, and the data should be helpful for modeling and diagnosing a variety of plasmas. [ABSTRACT FROM AUTHOR]

The spectra currently emerging from modern ground- and space-based astronomical instruments are of exceptionally high quality and resolution. To meaningfully analyse these spectra, researchers utilise complex modelling codes to replicate the observations. The main inputs to these codes are atomic data such as excitation and photoionisation cross sections, as well as radiative transition probabilities, energy levels, and line strengths. In this publication, the current capabilities of the numerical methods and computer packages used in the generation of these data are discussed. Particular emphasis is given to Fe-peak species and the heavy systems of tungsten and molybdenum. Some of the results presented to highlight certain issues and/or advances have already been published in the literature, while other sections present new recently evaluated atomic data for the first time.

An abundance of absorption and emission lines of iron-peak species such as Fe I and Fe II can be seen in the spectra of many astrophysical objects. Thus, the accurate modelling of such spectra requires sets of high quality atomic data for these species. In this paper, we present preliminary results from the present electron-impact excitation calculations for Fe II and fine-structure resolved photoionisation calculations for Fe I employing the Dirac atomic R-matrix and Breit–Pauli R-matrix methods. For the Fe II excitation, we compare results with all existing calculations, and for the Fe I photoionisation, we present a sample of level-resolved cross-sections. The calculations and results described throughout will be of use to those requiring high quality atomic data for modelling a wide variety of astrophysical objects.

Ni iv lines can be used as diagnostics for temperature and density for various astrophysical objects. In addition, ionization of Ni2+ is one of the causes of the opacity in the interstellar medium. We calculate the photoionization of Ni2+ and the electron-impact excitation of Ni3+. We use a fully-relativistic Dirac Atomic R-Matrix Code (DARC) method. We include a large set of configurations in the expansion of the wave functions of the target, up to the n=6 atomic shell. We show preliminary results for the photoionization cross-sections of Ni2+ and the electron-impact excitation collision strengths of Ni3+. The expected final results can be implemented in the available software packages for astrophysical plasma simulation, such as CLOUDY. We also show a preliminary estimation of the error of the data by the comparison of different sets of calculations.

The excitation cross sections of the 2S state of atomic hydrogen at 10 low incident electron energies (10.30 and 54.5 eV) have been calculated using the variational polarized method. Nine partial waves are used to get convergence of cross sections in the above energy range. The maximum of the cross section is 0.137 π a 0 2 at 11.14 eV which is close to the experimental result 0.163 ± 0.2 π a 0 2 at 11.6 ± 0.2 eV. The present results are compared with other calculations, many of them are based on the close-coupling approximation, including the R-matrix method. Differential cross sections at 13.6 eV incident energy have also been calculated. Spin-flip cross sections have been calculated and compared with those obtained using the close-coupling approximation.

We describe a theoretical approach to calculate the electron impact dynamics of atoms/ions placed in a dense plasma. The model takes into consideration that the continuous electron and the guest atom/ion are affected by a recently proposed (dense) plasma shielding parameter potential. As a test case, the present numerical method is employed to study the electron-impact excitation of He-like Ti XXI by using the distorted-wave wavefunction in the framework of the fully relativistic theory. The finite temperature and density effects as well as solid density plasma effects on the excitation energies, transition properties, and integrated cross sections are discussed in detail, which shed light on the shielding parameter potential in resolving practical problems. Results are compared with the available measurements and previous computations. The present work is not only providing a new implementation of the finite-temperature method by a self-consistent methodology, but also of great interest for the high energy density physics community, i.e., our results are of interest to the fusion researches. • We describe a theoretical approach to calculate the electron impact dynamics of atoms/ions in plasmas. • The finite temperature and density effects on the spectral characteristics are discussed. • This study is of interest for the high-energy density physics community. [ABSTRACT FROM AUTHOR]

Electron impact excitation in Ar + ions has been studied by using fully relativistic distorted wave theory. Calculations are performed to obtain the excitation cross-sections and rate-coefficients for the transitions from the ground state 3 p 5 ( J =3/2) to fine-structure levels of excited states 3 p 4 4 s , 3 p 4 4 p, 3 p 4 5 s , 3 p 4 5 p , 3 p 4 3 d and 3 p 4 4 d . Polarization of the radiation following the excitation has been calculated using the obtained magnetic sub-level cross-sections. Comparison of the present rate-coefficients is also done with the previously reported theoretical results for some unresolved fine structure transitions. [ABSTRACT FROM AUTHOR]

Abstract: Electron-impact excitation and resonant electron capture cross sections to the specific magnetic sublevels as well as the polarization of the strong (n=4, 5, 6) x-ray emitted from Ni-like through Ge-like tungsten ions have been studied systematically by using a fully relativistic distorted-wave method. We compare the polarizations for the same x-ray but from the above two different processes for the first time. It is found that the polarization degrees of x-ray following both the electron-impact excitation and the dielectronic recombination are totally different. Because the electron-impact excitation dominates in hot and dense plasmas and the dielectronic recombination plays a key role in low-density plasmas which are cooled and recombining by capturing continuum electrons, we hope that the specific plasmas conditions could be assessed by using these x-ray polarizations. [Copyright &y& Elsevier]

Highlights: [•] Laser assisted electron helium excitation is studied at low incident energies. [•] The inclusion of the second-order Born contributions is significant at low incident energies. [•] The target distortion induced by the laser field should be taken into account. [•] The effect of the second term of the Born series is reduced as the energy increases. [Copyright &y& Elsevier]

Abstract: The immense progress in the field of electron–atom scattering, where pure Coulomb potentials are involved, has been translated to collision processes in Debye plasmas. The Debye–Hückel potential is used to describe plasma Coulomb screening effects depending on the temperature and density of the plasma. We provide benchmark results of electron–helium scattering for momentum transfer cross sections, discrete excitation and ionization over a broad range of incident energies and Debye radii. [Copyright &y& Elsevier]

Abstract: A dipole-quadrupole electron-impact excitation model, consistent with molecular symmetry rules, is presented to fit ro-vibronic spectra of the hydrogen Fulcher-α Q-branch line emissions for passively measuring the rotational temperature of hydrogen neutral molecules in kinetic plasmas with the coronal equilibrium approximation. A quasi-rotational temperature and quadrupole contribution factor are adjustable parameters in the model. Quadrupole excitation is possible due to a violation of the 1st Born approximation for low to medium energy electrons (up to several hundred eV). The Born–Oppenheimer and Franck–Condon approximations are implicitly shown to hold. A quadrupole contribution of 10% is shown to fit experimental data at several temperatures from different experiments with electron energies from several to 100eV. A convenient chart is produced to graphically determine the vibrational temperature of the hydrogen molecules from diagonal band intensities, if the ground state distribution is Boltzmann. Hydrogen vibrational modes are long-lived, surviving up to thousands of wall collisions, consistent with multiple other molecular dynamics computational results. The importance of inter-molecular collisions during a plasma pulse is also discussed. [Copyright &y& Elsevier]

Results of experimental and theoretical investigation of electron-impact excitation of the 6 s 2 6 d   D 2 → 6 s 2 6 p   P 2 o spectral transitions from the ground 6 s 2 6 p   P 2 1 / 2 o level in the Pb+ ion are presented. The experimental excitation functions for the transitions, measured by a VUV spectroscopy method, using the crossed electron and ion beams technique, reveal a rather distinct resonance structure resulting mainly from the electron decay of both atomic and ionic autoionizing states. The absolute values of the emission cross-sections, obtained by normalizing the experimental data at the incident electron energy 100 eV by those calculated using the Flexible Atomic Code software package, were found to be (0.35 ± 0.17) × 10–16 cm2 for the 6 s 2 6 d   D 2 3 / 2 → 6 s 2 6 p   P 2 1 / 2 o (λ143.4 nm) transition and (0.19 ± 0.09) × 10–16 cm2 for the 6 s 2 6 d   D 2 5 / 2 → 6 s 2 6 p   P 2 3 / 2 o (λ182.2 nm) transition. [ABSTRACT FROM AUTHOR]

The modeling of non-local-thermodynamic-equilibrium plasmas is crucial for many aspects of high-energy-density physics. It often requires collisional–radiative models coupled with radiative-hydrodynamics simulations. Therefore, there is a strong need for fast and as accurate as possible calculations of the cross-sections and rates of the different collisional and radiative processes. We present an analytical approach for the computation of the electron-impact excitation (EIE) cross-sections in the Plane Wave Born (PWB) approximation. The formalism relies on the screened hydrogenic model. The EIE cross-section is expressed in terms of integrals, involving spherical Bessel functions, which can be calculated analytically. In order to remedy the fact that the PWB approximation is not correct at low energy (near threshold), we consider different correcting factors (Elwert–Sommerfeld, Cowan–Robb, Kilcrease–Brookes). We also investigate the role of plasma density effects such as Coulomb screening and quantum degeneracy on the EIE rate. This requires to integrate the collision strength multiplied by the Fermi–Dirac distribution and the Pauli blocking factor. We show that, using an analytical fit often used in collisional–radiative models, the EIE rate can be calculated accurately without any numerical integration, and compare our expression with a correction factor presented in a recent work. [ABSTRACT FROM AUTHOR]

The online atomic database of NORAD-Atomic-Data, where NORAD stands for Nahar OSU Radiative, is part of the data sources of the two international collaborations of the Opacity Project (OP) and the Iron Project (IP). It contains large sets of parameters for the dominant atomic processes in astrophysical plasmas, such as, (i) photo-excitation, (ii) photoionization, (iii) electron–ion recombination, (iv) electron–impact excitations. The atomic parameters correspond to tables of energy levels, level-specific total photoionization cross-sections, partial photoionization cross-sections of all bound states for leaving the residual ion in the ground state, partial cross-sections of the ground state for leaving the ion in various excited states, total level-specific electron–ion recombination rate coefficients that include both the radiative and dielectronic recombination, total recombination rate coefficients summed from contributions of an infinite number of recombined states, total photo-recombination cross-sections and rates with respect to photoelectron energy, transition probabilities, lifetimes, collision strengths. The database was created after the first two atomic databases, TOPbase under the OP and TIPbase under the IP. Hence the contents of NORAD-Atomic-Data are either new or from repeated calculations using a much larger wave function expansion making the data more complete. The results have been obtained from the R-matrix method using the close-coupling approximation developed under the OP and IP, and from atomic structure calculations using the program SUPERSTRUCTURE. They have been compared with available published results which have been obtained theoretically and experimentally, and are expected to be of high accuracy in general. All computations were carried out using the computational facilities at the Ohio Supercomputer Center (OSC) starting in 1990. At present it contains atomic data for 154 atomic species, 98 of which are lighter atomic species with nuclear charge Z ≤ 28 and 56 are heavier ones with Z > 28. New data are added with publications. [ABSTRACT FROM AUTHOR]

We develop a new relativistic model which can describe the dynamics on electron-impact excitation (EIE) of ions within a quantum plasma environment. An exemplary excitation 1 s 1/2 → 2 p 3/2 of Fe XXVI by electron impact with the exponential cosine-screened Coulomb potential (ECSCP) is presented, i.e., 25 times ionized atoms of Fe, exist in laser-produced plasmas, astrophysical objects, and electron beam ion trap experiments. For the atomic structure of target ion, using the same potential, a Ritz variational method with a trial wave function that contains unknown variational parameters is also proposed for comparison purposes. In this method, an analytical formula of bound energy is derived from the energy equation, and the variational parameters are determined by the minimization of the energy. The energies obtained from our two methods are compared with each other and other theoretical predictions based on the non-relativistic model and found to be in good agreement. For the collision dynamics, the continuum wave function is determined by solving the modified Dirac equations, in which the ECSCP is included for the solution of the continuum orbital. The total cross sections, magnetic sublevel cross sections, and the degrees of linear polarization of emitted x-rays are calculated as a function of the incident energy and screening parameter by using the distorted-wave method in the relativistic frame. Since there are no experiments or other calculations for EIE cross sections on this ion, the obtained results have been compared with those for an isolated ion. The effect of quantum plasma leads to a reduction in the total and magnetic sublevel cross-sections and thus reduces the degrees of linear polarization of emitted x-rays. Comparative analysis allows to estimate the quality of the proposed approximations. Our dynamic model is practicable and easy to apply, which may provide an alternative route towards information with fluorescence polarization in a quantum plasma environment. • We have developed a model to calculate the EIE process within a quantum plasma. • The present models compare well, with existing methods and experimental data. • The present results will be rewarding in interpreting the laboratory plasma. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The spectra currently emerging from modern ground- and space-based astronomical instruments are of exceptionally high quality and resolution. To meaningfully analyse these spectra, researchers utilise complex modelling codes to replicate the observations. The main inputs to these codes are atomic data such as excitation and photoionisation cross sections, as well as radiative transition probabilities, energy levels, and line strengths. In this publication, the current capabilities of the numerical methods and computer packages used in the generation of these data are discussed. Particular emphasis is given to Fe-peak species and the heavy systems of tungsten and molybdenum. Some of the results presented to highlight certain issues and/or advances have already been published in the literature, while other sections present new recently evaluated atomic data for the first time. [ABSTRACT FROM AUTHOR]

An abundance of absorption and emission lines of iron-peak species such as Fe I and Fe II can be seen in the spectra of many astrophysical objects. Thus, the accurate modelling of such spectra requires sets of high quality atomic data for these species. In this paper, we present preliminary results from the present electron-impact excitation calculations for Fe II and fine-structure resolved photoionisation calculations for Fe I employing the Dirac atomic R-matrix and Breit–Pauli R-matrix methods. For the Fe II excitation, we compare results with all existing calculations, and for the Fe I photoionisation, we present a sample of level-resolved cross-sections. The calculations and results described throughout will be of use to those requiring high quality atomic data for modelling a wide variety of astrophysical objects. [ABSTRACT FROM AUTHOR]