Pseudo-relativistic Hartree-Fock Research Articles

Radiative lifetime measurements and oscillator strength determination for transitions in singly ionized praseodymium (Pr II)

New radiative lifetimes for 20 levels of Pr II have been measured using the time-resolved laser-induced fluorescence (LIF) technique. The combination of these experimental values with theoretical branching fractions (BF) obtained with the pseudo-relativistic Hartree-Fock (HFR) approach has allowed us to determine oscillator strengths and transition probabilities for about 150 lines appearing in the spectral region between 369.9 and 741.2 nm. A detailed discussion of our new results and comparisons with previous data are also given in the present paper.

Radiative lifetime measurements and oscillator strengths of astrophysical interest in Ho III

Radiative lifetimes of three long-lived levels belonging to the 4f(10)5d configuration of Ho III have been measured, for the first time, using the time-resolved laser-induced fluorescence technique. A good agreement between the experimental lifetimes and theoretical results obtained within a multiconfigurational pseudo-relativistic Hartree-Fock (HFR) approach including core-polarization (CP) effects is observed provided an adequate scaling factor is applied to the transition matrix element. From the comparison theory-experiment, it has been possible to assess the reliability of the oscillator strengths of the 4f-5d transitions of astrophysical interest, particularly for the lines depopulating the levels considered in the present work. The present results fill in a gap concerning the f-values of doubly ionized holmium and are needed for a quantitative evaluation of the holmium abundance in some peculiar stars. (Less)

Isotope shiftstudies in Zr I by Doppler-free saturated absorptionspectroscopy and pseudo-relativistic Hartree-Fock calculations:I. Transitions 4d35s-4d25s5p

The isotope shifts of twelve Zr I 4d35s-4d25s5ptransitions in the green and the 4d35s a 5F5-4d35py 5G6 `reference' transitionat 468.78 nm have been determined by the technique of Doppler-free saturated absorption spectroscopy in a sputteredvapour. The specific mass shift (SMS) and the field shift (FS)contributions were separated using a King-plot analysis, inwhich the SMS of the 468.78 nm referencetransition was estimated from ab initio calculations.The 4d35s-4d25s5p transitions, which involve anelectron jump 4d→5p, represent an importantclass in which the SMS is large compared with the FS. This enables SMSs to bedetermined to high accuracy (1-2%), thus affording stringenttests of ab initio calculations. An interpretation ofthe isotope shifts was performed using refined multiconfigurational fine-structure calculations andpseudo-relativistic Hartree-Fock (PSUHFR) calculations. TheSMS values deduced from the PSUHFR calculationsare found to be systematically higher than the experimentalSMS values for all levels, by an average factor of 1.45±0.07 (where the uncertainty represents the standarddeviation of the distribution). Using PSUHFR estimates for theelectron density at the nucleus together with the experimentalFS for the 4d35s a 5F5-4d25s5p y 5G6 transition,the 90Zr-92Zr FSs for some relevantodd-parity configurations are predicted to be FS(4d35p)=-419 MHz, FS(4d25s6p) = + 281 MHz and FS(4d5s25p) = + 1012 MHz, relative to the lower-levelconfiguration 4d35s.

Measurement of radiative lifetimes and determination of transition probabilities of astrophysical interest in Ho iii

Lifetimes of six levels belonging to the 4f(10)6p configuration of Ho III have been measured for the first time using the time-resolved laser-induced fluorescence method. They are compared with multiconfigurational pseudo-relativistic Hartree-Fock calculations. A very good agreement is found. Using the experimental lifetimes and theoretical branching fractions, a first set of transition probabilities of astrophysical interest has been obtained for this ion.

Isotope shifts in hafnium from saturated-absorption spectroscopy

Isotope shifts of three lines of Hf I, lying in the red spectral region, have been measured by means of saturated-absorption spectroscopy in a hollow cathode. Combined with experimental data, previously given in the literature, and pseudo-relativistic Hartree-Fock estimates the field shifts (FS) of six relevant configurations are deduced: FS (5d26p2) = -84 mK, FS (6p26s2) = 36 mK, FS (5d6p26s) = -28 mK, FS (5d36p) = -90 mK, FS (5d4) = -94 mK and FS (5d6s26p) = 12 mK, referred to 5d26s2. For these three studied spectral lines, connecting the configurations 5d26s2 and 5d6s26p the specific mass shifts are estimated to lie between 5 and 8 times the normal shifts, using a King plot and pseudo-relativistic estimates for the Vinti integrals, respectively.

RHF-DFT approach for electron affinities of neutral atoms in groups 13 and 14

The pseudo-relativistic Hartree-Fock and density functional theory (DFT) has been used to calculate electron affinities of neutral atoms of the group-13 elements (B-, Al-, Ga-, In- and Tl-) and the group-14 elements (C-, Si-, Ge-, Sn- and Pb-). A simple approximate correlation-correction potential term derived from the DFT was added to the usual single-particle pseudo-relativistic Hartree-Fock Hamiltonian. In carrying out the calculations a novel scheme has been devised to obtain appropriate scaling factors for the Coulomb radial integrals of the group-14 elements. These same factors can be transportable without adjustment to the group-13 elements, on the basis of their similar electron pair correlation energies. The validity of our results is amply demonstrated by the consistency between our computed electron affinities and existing data. For the first four elements of group 13, our values are in good agreement with both the recent multi-configuration Dirac-Fock (MCDF) and the relativistic coupled-cluster (RCC) values. The electron affinity of 0.388 eV for the fifth element, Tl-, obtained in the present calculation is in better agreement with the RCC value (0.40±0.05 eV) than the MCDF value (0.291 eV).

Radiative lifetimes, branching fractions and transition probabilities in GeI -- solar implications

New radiative lifetimes have been measured for the 5s (3)P(0,1,2)degrees and 5s (1)P(1)degrees levels of Ge I using a laser-produced plasma subject to selective laser excitation. A diffraction grating based emission spectrometer of moderately high resolution has been used to remeasure the branching ratios of the 4p-5s depopulating transitions. The oscillator strengths of astrophysical interest, which have been derived from these new data, are compared with theoretical values calculated within a pseudo-relativistic Hartree-Fock approach. The new set of f-values has been compared with the few results available in the literature, which are generally characterized by a large scatter and a low accuracy. The solar photospheric abundance of germanium deduced from the new atomic data of the present work is A(Ge) = 3.58 +/- 0.05, on the usual logarithmic scale, in agreement with the meteoritic value. (Less)

Lifetime measurements in Yb II with time-resolved laser spectroscopy

Natural radiative lifetimes of 10 levels of singly ionized ytterbium have been measured with time-resolved laser spectroscopy. Free ions were produced in a laser-induced plasma. A stimulated Brillouin scattering technique has been used to produce laser pulses as short as 1 ns for the excitation of short-lived states. Pseudo-relativistic Hartree-Fock calculations, taking into account the core-polarization effects, have also been performed. A good agreement of the measured and the calculated lifetime values has been achieved.

Lifetime calculations in Yb II

Oscillator strengths and lifetime values for Yb II levels have been calculated within the framework of a pseudo-relativistic Hartree-Fock (HFR) approximation combined with a least-squares fitting of the calculated eigenvalues to the observed energy levels. A considerable amount of configuration interaction together with core-polarization effects have been included in the calculations. The quality of the HFR results has been assessed through a comparison with data obtained using the completely independent relativistic quantum defect orbital (RQDO) method. The theoretical lifetimes reported in the present paper are now in good agreement with most of the accurate experimental values available. The origin of the persisting discrepancies is suggested.

UV transitions of astrophysical interest in Ge II, As II and Se II

An extensive set of oscillator strengths and transition probabilities has been obtained for the UV transitions originating from the ground 4s24pn (n=1–3) states of Ge II, As II and Se II. These new data, calculated within the framework of a pseudo-relativistic Hartree–Fock (HFR) approach, fill in the gap existing in the atomic data needed for elemental abundance analysis of the interstellar medium. The f values are compared with the rather scarce results previously published in the literature. The astrophysical implications of the new transition rates regarding the interstellar medium are discussed.

Fine structure analysis of the even parity configuration system of Ti I

Even-parity configuration system of Ti I has been considered on the basis of the experimental data available in literature. The fine structure analysis has been performed with the aid of a linked-parameter method of level-fitting calculations in a large multiconfiguration basis. Fine structure parameters have been determined and precise wavefunctions of even energy levels have been evaluated. Appropriate pseudorelativistic Hartree-Fock ab initio calculations of fine structure parameters have been presented for comparison purposes. Configuration interaction effects on even-parity configurations have been discussed.

Transition probabilities for forbidden lines in Cr II

A detailed investigation of radiative transition probabilities has been performed for the magnetic dipole (M1) and electric quadrupole (E2) transitions involving the metastable energy levels within the 3d5 and 3d44s configurations of Cr II. The pseudo relativistic Hartree-Fock (HFR) method, combined with an optimization of radial parameters based on the available observed energy levels, has been used for the calculations.

Isotope shift investigations in the configurations 5d9nl and 5d8nln'l' of Pt I

The isotope shift in a platinum hollow cathode discharge was studied for transitions of the type 5d97s → 5d96p, 5d97s → 5d86s6p and 5d96p → 5d86s2 through laser optogalvanic spectroscopy and high resolution interferometry. Considering configuration mixing in each of the levels of 5d96s, 5d86s2, 5d86s6p and 5d96p of all known and the new evaluated level isotope shifts, we obtain average configuration isotope shift values for the even configurations ΔT(5d96s) = 2425 (90) MHz, ΔT(5d86s2) = 5960 (60) MHz, ΔT(5d97s) = 260 (160) MHz and for the odd configurations ΔT(5d96p) = −230 (380) MHz, ΔT(5d86s6p) = 2740 (250) MHz, ΔT(5d76s26p) = 9700 (4700) MHz. These experimental values compare well with the theoretically predicted configuration isotope shifts in platinum, based on pseudo-relativistic Hartree-Fock calculations.

Beam-laser lifetime measurements of Yb II energy levels.

Laser excitation of a fast beam of ${\mathrm{Yb}}^{+}$ ions has been used to make measurements of the radiative lifetimes of eight Yb ii energy levels, four of which were excited via transitions from the ion-trap metastable level 4${\mathit{f}}^{13}$6${\mathit{s}}^{2}$ $^{2}$${\mathit{F}}_{7/2}^{\mathit{o}}$. Comparison is made with the lifetimes that may be derived from the semiempirical pseudorelativistic Hartree-Fock calculation by Fawcett and Wilson [At. Data Nucl. Data Tables 48, 241 (1991)], the agreement being within 50% for seven of the eight levels considered.

Visible and near UV photon spectroscopy of charge-exchange collisions between Ar7+ and Li at 105 keV

Charge exchange collisions at 105 keV between Ar7+ ions and lithium atoms have been studied by photon spectroscopy in the 2000-6000 Å wavelength range. A large number of new lines in Ar VII have been identified with the help of ab initio pseudo-relativistic Hartree-Fock calculations taking into account electrostatic interactions between 3snl (n = 6–10), 3 pnl (n = 4–6) and 3dnl (n = 4) configurations. They correspond to transitions 3snl–3sn'l' with n = 7, 8, 9 and Δn = 1 and 2. Lines in Ar VI were also observed and identified as transitions 3s2nl–3s2n'l' and 3s3pnl–3s3pn'l'(n = 6, 7) and Δn = 1.

Measurement and interpretation of the odd-parity levels of Pb I.

We consider 51 odd-parity configurations of Pb i utilizing all data available from absorption and emission spectroscopy measurements, photoionization experiments, and ejected-electron spectroscopy. These include detailed results of our earlier laser spectroscopic studies of the 6${\mathit{s}}^{2}$6pns, 6${\mathit{s}}^{2}$6pnd, and 6${\mathit{s}}^{2}$6png Rydberg levels [P. Buch, J. Nellessen, and W. Ertmer, Phys. Scr. 38, 664 (1988)]. The analysis has been performed with the aid of a linked-parameter method of level-fitting calculations in a large multiconfiguration basis. New identifications of the 6s6${\mathit{p}}^{3}$ levels are proposed and reasons for their assignment are presented. On the basis of our level-fitting calculations precise assignments of 242 odd-parity electronic energy levels are given. Eigenvectors obtained in these calculations can be used to calculate the values of other physical observables with high precision. In addition, we have also made appropriate pseudorelativistic Hartree-Fock ab initio calculations of level structure, oscillator strengths, and autoionization widths for procedural guidance and comparison purposes.

Simple estimates of atomic negative ion structures

Ab initio calculation of electron affinities and level structures have been obtained by adding a simple approximate correlation-potential term to the usual pseudo-relativistic Hartree-Fock Hamiltonian. Results for the following systemsthe 2s2p2 and 2p3 configurations of Be− the p3 configurations of C−, Si−, Ge−, Sn− and Pb− the s2p and sp2 configurations of Mg−, Ca−, Sr−, Ba− and Ra− and the s2p and sp2 configurations of Zn−, Cd− and Hg−are reported here and compared, when possible, with earlier theoretical and experimental results.

Theoretical autoionization widths for the levels of the 4d95s25p configuration of Cd I

Pseudorelativistic Hartree-Fock radial wavefunctions have been used to provide ab initio estimates of discrete-continuum electrostatic interaction widths for all levels of the 4d95s25p configuration of Cd decaying into the 4d105s in p and 4d105 in f continua.

The ejected-electron spectra of manganese and samarium vapour atoms arising from autoionizing and Auger transitions following electron impact excitation

Autoionizing and Auger transitions in atomic manganese and samarium have been experimentally investigated by observation of the ejected electrons in the energy region 0 to 40 eV following electron impact excitation with incident beams in the energy range is 15-500 eV. Seventy-four spectral features are tabulated for manganese and a number of new assignments have been made based on pseudo-relativistic Hartree-Fock calculations and quantum defect analysis. A similar study of samarium reveals only a number of broad features in the ejected-electron energy range 8-10 eV. Three features have been observed consistently in the ejected-electron spectrum of samarium and assigned by comparison with previous work.

Pseudo-relativistic screening ratios for Re

Pseudo-relativistic Hartree-Fock calculations have been made for the (5d+6s) 7 and (5d+6s) 66p configurations of Re. These have been used to provide ab initio estimates of screening effects and specific mass isotope shifts. Such estimates are in good accord with recent experimental results.