Core Polarization Effects Research Articles

Perturbative role in the inelastic electron scattering from 29Si

Inelastic electron scattering form factors away from the closed sd -shell are investigated. This investigation covers the low-lying states in 29Si , which is considered according to the many-particle configuration mixing shell model as the 16O core, plus thirteen nucleons distributed over the entire sd -shell orbits. The investigation concentrates on the perturbative role of the core, which is called core polarization effects, on the inelastic electron scattering form factors. Core polarization effects are taken into consideration through the excitation of nucleons from 1s and 1p core orbits, and also from the 2s -1d valence orbits into higher shells, with 2ℏω excitations. Core polarization matrix elements are calculated with the M3Y effective interaction. For the sd -shell model space, a new Hamiltonian, based on a renormalized G -matrix, USDB, is used. All calculations are performed without adjusting any parameters.

Multiconfiguration Dirac–Hartree–Fock energies and transition probabilities for [formula omitted] transitions in Ne II

Multiconfiguration Dirac–Hartree–Fock energies, lifetimes, and transition probabilities for transitions between 2 p 4 ( P 3 ) 3 d and 2 p 4 ( P 3 ) 4 f levels of Ne II are reported from calculations that included the effect of core-polarization. Transition energies are in excellent agreement with observed values. For many transitions the length and velocity gauge results agree within a fraction of a percent. Transition probabilities are compared with experimental values and the Coulomb approximation.

Experimental and theoretical transition probabilities in singly ionized gold

Absolute transition probabilities have been measured for lines originating from the 5d 9 6d and 5d 9 7s electronic configurations in the spectrum of singly ionized gold (Au II). The laser-induced breakdown spectroscopy has been applied to free gold atoms and ions produced by laser ablation. Absolute transition probabilities have been determined using the branching fraction and the Boltzmann plot methods. Theoretical branching fractions as well as radiative lifetime values have also been obtained by a relativistic Hartree-Fock method taking core polarization and configuration interaction effects into account. The new results are compared with previous results when available.

Core-excitation effects on atomic transitions

By including explicitly the electronic configurations with three simultaneously excited electronic orbitals, we have successfully extended the BSCI (B-spline based configuration interaction) method to estimate directly the effects of inner shell core-excitation to atomic transitions. In particular, we are able to carry out detailed ab initio investigation on the core polarization effects without the need of employing parameterized model potential. We present in this paper quantitatively the change in atomic transition rate due to the core excitations for four-electron systems, especially for transitions involving doubly excited states and transitions with small oscillator strengths. Our numerical results using length and velocity gauge typically agree to better than 1%.

Rigorous ab initio study of Allowed and Forbidden transition amplitudes of T12+

We report here 'allowed' and 'forbidden' electromagnetic transition amplitudes among various low lying states of doubly ionized Thallium (T12+) using relativistic coupled cluster method based on Dirac-Fock hybrid basis functions. These transitions are of importance in astrophysics and plasma research. The effect of core correlation, pair correlation and core polarization on these transitions are estimated.

Atomic data for radioactive elements Ra I, Ra II, Ac I and Ac II and application to their detection in HD 101065 and HR 465

Radiative data for transitions of astrophysical interest in radioactive elements Ra I, Ra II, Ac I and Ac II have been computed using a semi-empirical relativistic Hartree-Fock approach including core polarization effects. Most of the oscillator strengths reported in the present paper are new. A possible detection of radium (Ra II) and actinium (Ac II) in the spectrum of the stars HD 101065 and HR 465 is examined and discussed.

Calculations of transition and permanent dipole moments of heteronuclear alkali dimers NaK, NaRb and NaCs

Obtaining ultracold samples of dipolar molecules is a current challenge which requires an accurate knowledge of their electronic properties to guide the ongoing experiments. In this paper, we calculate permanent dipole moments and transition dipole moments for excited states for alkali dimers NaK, NaRb and NaCs using a standard quantum chemistry approach based on pseudopotentials for atomic core representation, Gaussian basis sets, and effective terms for core polarization effects. We provide an extensive set of data concerning transitions among the first seven molecular states of each symmetry 1Σ+, 3Σ+, 1Π, 3Π. The accuracy of our results is generally improved compared to previous similar calculations on NaK, while they are found to be in good agreement with the few NaRb states calculated with other methods. Results for NaCs transition dipole moments are given here for the first time.

Lifetime and transition probability determination in xenon ions

Radiative lifetimes have been calculated for 15 levels of Xe VII belonging to the configurations 5s5p, 5p2, 5s5d, 5s6s, 5p5d, 4f5p, 5p5d and 5s5f and for 4 levels of the 5p and 5d configurations of Xe VIII. A relativistic Hartree-Fock approach including core-polarization effects, on the one hand, and a purely relativistic multiconfiguration Dirac-Fock method, on the other hand, have been used for the calculations. The accuracy of the present set of results has been assessed through comparisons with radiative lifetime measurements obtained by beam-foil spectroscopy. A good agreement between theory and experiment is observed for most of the levels. A new set of transition probabilities is proposed for 169 transitions of Xe VII and 45 transitions of Xe VIII.

Enhanced role of electron correlation in the hyperfine interactions inD5∕22states in alkaline-earth-metal ions

The low-lying n(=3,4,5)d $^2D_{5/2}$ states alkaline earth ions are of vital importance in a number of different physical applications. The hyperfine structure constants of these states are characterized by unusually strong electron correlation effects. Relativistic coupled-cluster theory has been employed to carry out {\it ab initio} calculations of these constants. The role of the all order core-polarization effects was found to be decisive in obtaining good agreement of the results of our calculations with accurate measurements. The present work is an apt demonstration of the power of the coupled-cluster method to cope with strongly interacting configurations.

Effects on intercombination transition rates and branching ratios—the UV0.01 (3s23p2 3P1,2 − 3s3p3 5S2) multiplet in Si I-like ions revisited

We report on large-scale ab initio calculations for intercombination lines in Si I-like ions. Two measurable quantities, the lifetime of the 3s3p3 5S2 level and the branching ratio of the two lines are discussed, to infer the importance of different features of our calculations. The effects of core polarization, two-body spin-dependent operators and Dirac contra Breit–Pauli approaches are discussed. Earlier calculations are reviewed and evaluated. The calculated lifetimes are in good agreement with experiments, while a discrepancy persists for branching ratios.

Radiative parameters for some transitions arising from the 3d94d and 3d84s2 electronic configurations in Cu II spectrum

Transition probabilities of 41 transitions originating from the 3d94d and 3d84s2 electronic configurations of singly ionized copper have been determined using laser-induced breakdown spectroscopy. The Cu II ions have been produced by laser ablation. The experimental relative transition probabilities have been converted into an absolute scale using measured branching fractions and theoretical radiative lifetimes of the corresponding upper states obtained by a relativistic Hartree–Fock method taking core-polarization and configuration interaction effects into account. Comparison of the new results with previously available data is also presented.

Transition probabilities and lifetimes for atoms and ions from the sixth row of the periodic table and the database DESIRE

We have started a systematic investigation of the radiative properties of the elements of the sixth row of the periodic table. Using a combination of experimental radiative lifetimes obtained with the time-resolved laser-induced fluorescence (LIF) technique and of theoretical branching fractions (BF) calculated with a HFR approach taking configuration interaction and core-polarization effects into account, transition probabilities have been deduced for a number of transitions of astrophysical interest. So far results have been obtained for the elements Ta, Re, Os, Ir, Tl or Au or their ions. The results obtained are stored in the database DatabasE for the SIxth Row Elements (DESIRE), an extension of the database DREAM, which will be progressively created on a web site of the University of Mons-Hainaut in Belgium. In the present paper, some emphasis is put on the procedures followed to obtain the new results but also on the difficulties associated with their determination.

Transition probabilities in complex ions: The case of americium

We report on the first calculations of transition probabilities in neutral americium, a heavy radioactive element belonging to the actinide group. A relativistic Hartree–Fock approach, including core-polarization effects, has been used for obtaining branching fractions and radiative lifetimes for some low-lying levels belonging to the 7s7p configuration. A comparison with the few experimental results available shows reasonable agreement between theory and experiment.

Transition probabilities and lifetimes in gold (Au I and Au II)

Radiative lifetimes of three odd-parity levels of neutral gold (Au I) and one odd-parity level of singly ionized gold (Au II), measured using the time-resolved laser-induced fluorescence technique, have allowed the testing of the reliability of a relativistic Hartree–Fock model of the atomic structure taking configuration interaction and core-polarization effects into account. The importance of the inclusion of the latter effects in the calculations is emphasized. The laser-induced fluorescence lifetimes, combined with the theoretical branching fractions, have allowed us to deduce oscillator strengths for six 5d96s2–5d96s6p and 5d106s–5d96s6p transitions of Au I and for sixty-three 5d96s–5d96p, 5d96p–5d97s and 5d10–5d96p UV transitions of Au II.

Relativistic coupled-cluster theory of quadrupole moments and hyperfine structure constants of5dstates inBa+

The narrow optical frequency resonances of the $6s\phantom{\rule{0.2em}{0ex}}^{2}S_{1∕2}\ensuremath{\rightarrow}5d\phantom{\rule{0.2em}{0ex}}^{2}D_{3∕2}$ and $6s\phantom{\rule{0.2em}{0ex}}^{2}S_{1∕2}\ensuremath{\rightarrow}5d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}$ forbidden transitions in ${\mathrm{Ba}}^{+}$ have been proposed as suitable frequencies for a new optical frequency standard. The major sources of errors in measurements of singly ionized systems are due to the quadratic Zeeman and electric quadrupole shifts. We report here the most accurate calculations to date for the hyperfine structure constants and electric-quadrupole moments of the $5d\phantom{\rule{0.2em}{0ex}}^{2}D_{3∕2}$ and $5d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}$ states in ${\mathrm{Ba}}^{+}$, which determine the quadratic Zeeman and electric quadrupole shifts. Relativistic coupled-cluster theory has been employed to calculate these quantities and large electron correlation effects are observed. It is also shown that for the high accuracy calculation of the $5d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}$ state in ${\mathrm{Ba}}^{+}$, all order core polarization effects play a significant role.

Radiative lifetime measurements and semi-empirical transition probability calculations in neutral rhenium

Radiative lifetimes of 11 odd-parity levels of neutral rhenium (Re I) were measured using time-resolved laser-induced fluorescence techniques. For ten levels, there were no previous results available. The new results have been used to assess the accuracy of calculations with a Hartree–Fock-plus-relativistic-corrections model that takes configuration interaction and core-polarization effects into account and they have allowed the deduction of reliable semi-empirical transition probabilities for 81 Re I lines.

Radiative lifetimes, branching fractions and oscillator strengths in Pd I and the solar palladium abundance

Transition probabilities have been derived for 20 5s−5p transitions of Pd I from a combination of radiative lifetime measurements for 6 odd-parity levels with time-resolved laser-induced fluorescence spectroscopy and of branching fraction determination using a hollow cathode discharge lamp. Additional oscillator strengths for 18 transitions have been determined from measured lifetimes and theoretical branching fractions obtained from configuration interaction calculations with core-polarization effects included. These new results have allowed us to refine the palladium abundance in the solar photosphere: APd = 1.66 ± 0.04, in the usual logarithmic scale, a result in close agreement with the meteoritic value.

Radiative Lifetimes and Transition Probabilities of Astrophysical Interest in Zr II

Radiative lifetimes of 16 odd levels belonging to the 4d(2)5p configuration of Zr II have been measured using a time-resolved laser-induced fluorescence technique with a single-step excitation process either from the ground state or from metastable levels belonging to the 4d(2)5s and 4d(3) configurations. For 12 levels, there were no previous results available. The new experimental results and the lifetime values available in the literature have allowed to test a theoretical relativistic Hartree-Fock (HFR) model including core-polarization effects and to deduce transition probabilities for 242 transitions of astrophysical interest in the range 187.8-535.0 nm.

Transition probabilities and lifetimes in neutral and singly ionized osmium and the Solar osmium abundance

Radiative lifetime measurements have been performed, with a time-resolved laser-induced fluorescence technique, for 12 levels of Os I and for 9 levels of Os II. For 9 levels of Os I and 4 levels of Os II, there were no previous experimental data available. From a comparison with new theoretical calculations, taking configuration interactions and core-polarization effects into account, it has been possible to deduce oscillator strengths for 129 transitions of Os I and 137 transitions of Os II of astrophysical interest appearing in the wavelength range 180.0–870.0 nm. These results have allowed us to revise the abundance of osmium in the solar photosphere (log eOs = 1.25 ± 0.11). The newly derived oscillator strengths have been applied as well to derive the osmium abundance in the carbon-rich metal-poor star HD 187861.

Radiative parameters for some transitions in the spectrum of Ag ii

Radiative parameters for transitions depopulating the levels belonging to the 4d85s2, 4d96s and 4d95d configurations of Ag ii have been obtained from a combination of theoretical lifetimes and experimental branching fractions. On the experimental side, a laser-produced plasma was used as a source of Ag+ ions. The light emitted by the plasma was analysed by a grating monochromator coupled with a time-resolved optical multichannel analyser system. Spectral response calibration of the experimental system was performed using a deuterium lamp in the wavelength range from 200 to 400 nm, and a standard tungsten lamp in the range from 350 to 600 nm. The transition probabilities were obtained from measured branching ratios and theoretical radiative lifetimes of the corresponding states calculated with a relativistic Hartree-Fock approach including core-polarization effects and configuration interaction in an extensive way. Theoretical and experimental data have been compared and the new data have also been compared with the few previous results available in the literature.