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Radiative decay rates are obtained for the first time for allowed (E1) and forbidden (M1, E2) transitions in trebly ionized tungsten (W IV). Our calculations, motivated by strong interest for low-density plasmas and fusion research, illustrate in a convincing way the importance of core-valence correlation effects which substantially increase the lifetimes and, accordingly, decrease the transition probabilities of this heavy ion. Due to the lack of experimental data for WIV, the reliability of the theoretical 'f' values can only be tested by comparison of numerical results obtained with two independent (i.e. multiconfiguration Dirac-Fock and relativistic Hartree-Fock with core-polarization effects (HFR+CPOL)) methods well suited for investigating the atomic structure of heavy ions. [ABSTRACT FROM AUTHOR]

Aims. This work reports oscillator strengths for transitions of astrophysical interest in singly ionized rhodium. Methods. Seventeen radiative lifetimes in Rh+ have been measured with the time-resolved laser-induced fluorescence technique and combined with theoretical branching fractions calculated using a relativistic Hartree-Fock model including core-polarization effects to obtain oscillator strengths. Results. On the basis of the good agreement between theory and experiment for the lifetimes, new reliable oscillator strengths have been deduced for a set of 113 Rh II transitions in the spectral range 153-418 nm [ABSTRACT FROM AUTHOR]

Radiative lifetimes of 16 odd levels belonging to the 4d25p 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 4d25s and 4d3 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Radiative lifetime measurements were performed with time-resolved laser-induced fluorescence techniques for 24 levels of Nd ii in the energy range 20 500–32 500 cm−1. For 17 levels, no previous experimental data exist. These results have allowed the testing of new theoretical calculations with the relativistic Hartree–Fock method taking configuration interactions and core-polarization effects into account, and a satisfying agreement has been found for this complex ion. A new set of calculated oscillator strengths, accurate within a few per cent for the strongest transitions, is presented for 107 lines of astrophysical interest appearing in the wavelength range 358.0–1100.0 nm. These results will be useful to evaluate abundance values of neodymium in chemically peculiar stars in relation with cosmochronology. [ABSTRACT FROM AUTHOR]

ABSTRACT A set of transition probabilities has been calculated for Eu iii transitions of astrophysical interest particularly for the study of chemically peculiar stars. They were obtained taking configuration interaction and core-polarization effects into account. The accuracy of the new scale of oscillator strengths, which differs substantially from previous results, has been assessed through comparisons with recent time-resolved laser-induced fluorescence measurements of radiative lifetimes. [ABSTRACT FROM AUTHOR]

Abstract The importance of core-polarization effects on oscillator strength determination in Ce iii is emphasized. The inclusion of these effects in relativistic Hartree–Fock (HFR) calculations leads to theoretical lifetime values for some 4f6p levels of this ion in close agreement with recent time-resolved laser-induced fluorescence measurements. These new atomic data, the most accurate to date, have allowed the refinement of the stellar abundance determination of cerium in the chemically peculiar star HD 192913, but have not altered in a drastic way the conclusions derived in recent analyses regarding the overabundance of this element. [ABSTRACT FROM AUTHOR]

The lifetimes of three short-lived levels belonging to the 4f[sup 9]6p configuration and of two long-lived levels of the 4f[sup 9]5d configuration of Dy iiihave been measured for the first time using time-resolved laser-induced fluorescence techniques. They are in good agreement with theoretical values calculated within the framework of a pseudo-relativistic configuration interaction approximation. Using the experimental lifetimes and the theoretical branching fractions, a first set of transition probabilities of astrophysical interest has been obtained for Dy iii. [ABSTRACT FROM AUTHOR]

Lifetimes of six levels belonging to the 4f[sup 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. [ABSTRACT FROM AUTHOR]

Radiative lifetimes of seven excited states of Er iii have been measured using time-resolved laser-induced fluorescence following two-photon excitation. Relativistic Hartree–Fock calculations taking core-polarization effects into account are found to be in excellent agreement with the experimental results. A large set of new calculated transition probabilities is presented for many transitions of astrophysical interest. These results will be useful for investigating the composition of chemically peculiar stars. [ABSTRACT FROM AUTHOR]

Natural radiative lifetimes have been measured for three odd-parity levels of neutral lead using time-resolved UV laser-induced fluorescence from a laser-produced plasma. These new lifetimes, as well as additional recent values obtained by laser spectroscopy, combined with theoretical branching ratios deduced from a relativistic Hartree–Fock calculation taking core polarization effects into account, have allowed the deduction of a new set of accurate f-values of astrophysical interest. Using the new lifetime value for 6p7s (1/2, 1/2)°[sub 0], a refined value of the lead abundance in the solar photosphere is deduced: A[sub Pb] = 2.00±0.06 on the usual logarithmic scale, allowing the resolution of the long-standing discrepancy previously observed between the solar photosphere and meteorites. [ABSTRACT FROM AUTHOR]

By a combination of radiative lifetimes measured using the fast-beam-laser method and experimental branching ratios deduced from Fourier transform spectrometer spectra, it has been possible to derive experimental f-values for Lu ii lines observed in the visible and near-ultraviolet regions. These data are compared with relativistic Hartree–Fock calculations, taking core polarization effects into account, and a set of additional oscillator strengths of astrophysical interest is presented. [ABSTRACT FROM AUTHOR]

Absolute transition probabilities are calculated for 2 p( P) nd − 2 p( P) n′f transitions of C i (1 ⩽ λ ⩽ 3 μ). Pair coupling expressions for line strengths are used and the radial wavefunctions are obtained through the use of the Coulomb approximation. A description of the occurrence of these lines in the solar photospheric spectrum is presented and 47 new identifications are proposed. [ABSTRACT FROM AUTHOR]