Engineering topics

Quinet, Pascal

Publications and source records attributed to Quinet, Pascal.

10 records

DOE OSTI2019

Energy levels, weighted oscillator strengths, transition rates, lifetimes, hyperfine structures and isotope shifts of He-like-Sn deduced from the relativistic multiconfiguration Dirac–Hartree–Fock and second-order many-body perturbation theory calculations

We disclose relativistic multiconfiguration Dirac–Hartree–Fock (MCDHF) spectrum calculations for SnXLIX. Energy levels, weighted oscillator strengths, isotope shifts, hyperfine structure and Landé g{sub J} factors are calculated for 127 odd- and even-parity states as well as lifetimes and transition rates between these states. To scrutinize the accuracy of our results, we have implemented parallel calculations using a Flexible Atomic Code (FAC) by introducing the Second-Order Many-Body Perturbation Theory (MBPT) method. Additionally, the Breit interaction and leading quantum electrodynamic effects (QED) are included as perturbations in extensive relativistic configuration interaction (RCI) calculations. We signal that, our calculations for SnXLIX are made for the first time and they provide to date the most accurate and complete atomic data related to this ion.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2019

Multiconfiguration Dirac–Hartree–Fock energy levels, weighted oscillator strengths, transitions probabilities, lifetimes, hyperfine constants, Landé g-factors and isotope shifts of Xe LIII

Energy levels, weighted oscillator strengths and transition probabilities, lifetimes, hyperfine interaction constants, Landé g{sub J} factors and isotope shifts are calculated for all levels of 1s{sup 2} and 1snl (n=2−7) configurations of He-like xenon ion (Xe LIII). Multiconfigurational Dirac–Hartree–Fock (MCDHF) method is adopted for calculating these spectroscopic data. Comparisons are made with similar data obtained with FAC (Flexible Atomic Code) to assess the accuracy of the results. Transition probabilities are reported for all E1, E2, M1 and M2 transitions from the ground level. Breit interactions and quantum electrodynamics effects are estimated in extensive Relativistic Configuration Interaction (RCI) calculations. Comparisons were made with the available data in the literature and good agreement was found which confirms the reliability of our results. The accuracy of the present calculations is high enough to facilitate identification of many observed spectral lines. Almost all atomic data of He-like xenon ion presented in this paper are calculated for the first time.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2018

Second spectrum of Chromium (Cr II) Part I: New energy level reanalysis

Using a linked-parametric technique of level-fitting calculations in a multiconfiguration basis, a parametric fine structure (fs) analysis for both even and odd parities of Cr II was achieved. For the first time the fs parameter, magnetic Landé g-factor and the percentage of leading eigenvector values for more than one thousand levels are determined and given for these two sets. This study has led us to confirm in the whole the well founded basis of NIST team works but inevitably also to exchange assignments of some levels classified in earlier lists of energy levels and to shift positions of some quartets like {sup 4}F{sub J} for instance. Furthermore we take this opportunity to add our predicted doublet, quartet and sextet locations for missing experimental levels up to 124,000 cm{sup −1}.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2018

Second spectrum of chromium (Cr II), Part III: Radiative lifetimes and transition probabilities from highly excited 3d{sup 4}5s levels

In this study we have extended our previous investigations of Cr II spectrum to levels of the 3d{sup 4}5s configuration. Once again an overall good agreement is observed for these levels between experimental oscillator strength values and our calculated data using two different approaches, namely the oscillator strength parameterization and the HFR+CPOL methods. Recurring to the latter model we have computed radiative lifetime values for 20 3d{sup 4}5s levels, confirming the well founded basis of recent experimental data, given in literature. From the use of the former method and with the help of a least squares fitting procedure to available experimental gf-values we have taken advantage of extracting for the first time the transition radial integral value for 3d{sup 4}4p−3d{sup 4}5s, 〈4p|r{sup 1}|5s〉=1.962±0.005, which is confirmed favorably by ab initio results, obtained by the HFR method scaled by a factor 0.92 or directly by the HFR+CPOL approach. Finally a long list of semi-empirical oscillator strength, transition probability and branching fraction values is generated for around 500 Cr II transitions depopulating the 3d{sup 4}5s levels. Our new gf data are compared successfully with those given by Kurucz.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2018

Second spectrum of Chromium (Cr II), Part II: Radiative lifetimes and oscillator strengths of transitions depopulating low lying 3d{sup 4}4p levels

Radiative lifetime and oscillator strength values were computed by means of a pseudo-relativistic Hartree–Fock model including core-polarization and compared successfully with experimental data given in the literature for respectively numerous low-lying Cr II 3d{sup 4}4p levels, up to 54784 cm{sup −1}, and transitions depopulating these levels. Then transition probability and branching fraction data were also deduced in the wavelength range 1825–94400 Å. Furthermore the extracted radial integral values, obtained with the help of the oscillator strength parameterization method, are given for involved transitions in this work, i.e. 3d{sup 4}4s–3d{sup 4}4p, 3d{sup 5}–3d{sup 4}4p and 3d{sup 4}4p–3d{sup 4}4d. We confirm our observed previous general trends, noting once again a decreasing of transition radial integral values with filling nd shells of the same principal quantum numbers for nd{sup k}(n+1)s → nd{sup k}(n+1)p transitions.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2016

DETECTION OF FORBIDDEN LINE COMPONENTS OF LITHIUM-LIKE CARBON IN STELLAR SPECTRA

We report the first identification of forbidden line components from an element heavier than helium in the spectrum of astrophysical plasmas. So far, these components were identified only in laboratory plasmas and not in astrophysical objects. Forbidden components are well known for neutral helium lines in hot stars, particularly in helium-rich post-AGB stars and white dwarfs. We discovered that two hitherto unidentified lines in the ultraviolet spectra of hot hydrogen-deficient (pre-) white dwarfs can be identified as forbidden line components of triply ionized carbon (C iv). The forbidden components (3p–4f and 3d–4d) appear in the blue and red wings of the strong, Stark broadened 3p–4d and 3d–4f lines at 1108 Å and 1169 Å, respectively. They are visible over a wide effective temperature range (60,000–200,000 K) in helium-rich (DO) white dwarfs and PG 1159 stars that have strongly oversolar carbon abundances.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

Atomic data and spectral model for Fe II

We present extensive calculations of radiative transition rates and electron impact collision strengths for Fe ii. The data sets involve 52 levels from the 3d{sup 7}, 3d{sup 6}4s, and 3d{sup 5}4s{sup 2} configurations. Computations of A-values are carried out with a combination of state-of-the-art multiconfiguration approaches, namely the relativistic Hartree–Fock, Thomas–Fermi–Dirac potential, and Dirac–Fock methods, while the R-matrix plus intermediate coupling frame transformation, Breit–Pauli R-matrix, and Dirac R-matrix packages are used to obtain collision strengths. We examine the advantages and shortcomings of each of these methods, and estimate rate uncertainties from the resulting data dispersion. We proceed to construct excitation balance spectral models, and compare the predictions from each data set with observed spectra from various astronomical objects. We are thus able to establish benchmarks in the spectral modeling of [Fe ii] emission in the IR and optical regions as well as in the UV Fe ii absorption spectra. Finally, we provide diagnostic line ratios and line emissivities for emission spectroscopy as well as column densities for absorption spectroscopy. All atomic data and models are available online and through the AtomPy atomic data curation environment.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2010

Experimental and theoretical lifetimes and transition probabilities in Sb i

We present experimental atomic lifetimes for 12 levels in Sb i. The levels belong to the 5p{sup 2}({sup 3}P)6s {sup 2}P, {sup 4}P, and 5p{sup 2}({sup 3}P)5d {sup 4}P, {sup 4}F, and {sup 2}F terms. The lifetimes were measured using time-resolved laser-induced fluorescence. In addition, we report calculations of transition probabilities in Sb i using a multiconfigurational Dirac-Hartree-Fock method. The physical model was tested through comparisons between theoretical and experimental lifetimes for 5d and 6s levels. The lifetimes of the 5d {sup 4}F{sub 3/2,5/2,7/2} levels (19.5, 7.8, and 54 ns, respectively) depend strongly on the J value. This is explained by different degrees of level mixing for the different levels in the {sup 4}F term.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2010

Radiative-lifetime measurements and calculations of odd-parity highly excited levels in Ba i

Natural radiative lifetime measurements have been performed for 70 odd-parity highly excited levels of neutral barium in the energy range from 308 15.512 to 417 59.93 cm{sup -1} by a time-resolved laser-induced fluorescence technique in a laser-produced plasma. The lifetime values measured in this paper are in the range from 11.3 to 901 ns. They are compared with the published lifetimes of four levels. Two of them are in good agreement, whereas for the other two our measurements are slightly longer than the published data. The reasons for the discrepancies are discussed. Comparisons with theoretical results of the Hartree-Fock method with relativistic corrections illustrate the difficulties associated with the use of Cowan's codes for obtaining accurate branching fractions for transitions depopulating highly excited levels along the Rydberg series of heavy neutral elements. This work will be useful to extend the set of oscillator strengths available in Ba i.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2010

ATOMIC DATA AND SPECTRAL MODEL FOR Fe III

We present new atomic data (radiative transitions rates and collision strengths) from large-scale calculations and a non-LTE spectral model for Fe III. This model is in very good agreement with observed astronomical emission spectra, in contrast with previous models that yield large discrepancies in observations. The present atomic computations employ a combination of atomic physics methods, e.g., relativistic Hartree-Fock, the Thomas-Fermi-Dirac potential, and Dirac-Fock computation of A-values and the R-matrix with intermediate coupling frame transformation and the Dirac R-matrix. We study advantages and shortcomings of each method. It is found that the Dirac R-matrix collision strengths yield excellent agreement with observations, much improved over previously available models. By contrast, the transformation of the LS-coupling R-matrix fails to yield accurate effective collision strengths at around 10{sup 4} K, despite using very large configuration expansions, due to the limited treatment of spin-orbit effects in the near-threshold resonances of the collision strengths. The present work demonstrates that accurate atomic data for low-ionization iron-peak species are now within reach.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗