V. Fivet

Lifetime measurements and calculated transition probabilities in W III

New experimental lifetimes for two levels in doubly ionized tungsten, W III, have been obtained using the time-resolved laser-induced-fluorescence technique. Theoretical oscillator strengths obtained from a HFR calculation including the effects of core-polarization are reported for all transitions from levels below E 2, thus greatly extending our knowledge of the radiative data in W III. Good agreement is found between the calculated lifetimes and the experimental values from this and previous works. These new results fill a gap in the available data for this ion which is expected to play an important role in fusion reactors.

Transition probabilities of astrophysical interest in the niobium ions Nb+ and Nb2+

Aims. We attempt to derive accurate transition probabilities for astrophysically interesting spectral lines of Nb ii and Nb iii and determine the niobium abundance in the Sun and metal-poor stars rich in neutron-capture elements. Methods. We used the time-resolved laser-induced fluorescence technique to measure radiative lifetimes in Nb ii. Branching fractions were measured from spectra recorded using Fourier transform spectroscopy. The radiative lifetimes and the branching fractions were combined yielding transition probabilities. In addition, we calculated lifetimes and transition probablities in Nb ii and Nb iii using a relativistic Hartree-Fock method that includes core polarization. Abundances of the sun and five metal-poor stars were derived using synthetic spectra calculated with the MOOG code, including hyperfine broadening of the lines. Results. We present laboratory measurements of 17 radiative lifetimes in Nb ii. By combining these lifetimes with branching fractions for lines depopulating the levels, we derive the transition probabilities of 107 Nb ii lines from 4d 3 5p configuration in the wavelength region 2240−4700 A. For the first time, we present theoretical transition probabilities of 76 Nb III transitions with wavelengths in the range 1430−3140 A. The derived solar photospheric niobium abundance log � � = 1.44 ± 0.06 is in agreement with the meteoritic value. The stellar Nb/Eu abundance ratio determined for five metal-poor stars confirms that the r-process is a dominant production method for the n-capture elements in these stars.

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 5d(9)6s(2)-5d(9)6s6p and 5d(10)6s-5d(9)6s6p transitions of Au I and for sixty-three 5d(9)6s-5d(9)6p, 5d(9)6p-5d(9)7s and 5d(10)-5d(9)6p UV transitions of Au II. (Less)

Lifetime measurements in Ru II and calculated oscillator strengths in Ru II and Ru III

A new set of theoretical f-values is reported for 178 Ru II transitions of astrophysical interest, involving energy levels below 58 000 cm−1. The theoretical model, including core-polarization effects, has been tested by comparing theoretical lifetimes with new measurements performed by time-resolved laser-induced fluorescence spectroscopy for 23 4d6(5D)5p odd levels of Ru II and by comparing theoretical and experimental Lande g-factors. The first set of transition probabilities is proposed for 25 strong lines depopulating the 4d55p5,7P° terms of Ru III. The new results will allow quantitative investigations of stellar spectra and allow the astrophysicists to refine the ruthenium abundance in stars.

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.

Radiative lifetime measurements and calculations in doubly ionized tantalum (Ta III)

Radiative lifetimes of six odd-parity levels belonging to the 5d 2 6p configuration of doubly ionized tantalum (Ta III) have been measured using the time-resolved-laser-inducedfluorescence technique. Supporting theoretical calculations, including core-polarization effects, have been performed to model configuration interaction and to estimate branching fractions. The excellent agreement between the theoretical and experimental lifetimes allows us to assess the reliability of the 206 calculated transition probabilities. It is expected that this new set of results will be useful to astrophysicists for the investigation of the chemical composition of stars.

Relativistic Hartree-Fock and Dirac-Fock atomic structure calculations in Fr-like ions Ra+, Ac2+Th3+ and U5+

A detailed investigation of radiative parameters for electric dipole (E1) transitions is presented for the ions Ra II, Ac III, Th IV and U VI along the francium isoelectronic sequence. The pseudo-relativistic Hartree–Fock (HFR) method including core-polarization effects is used for the calculations. Comparisons with multiconfigurational Dirac–Fock (MCDF) calculations show that the most important relativistic effects are taken into account. In view of their importance in nuclear laser spectroscopy, forbidden rates (transitions M1 and E2) in Th IV are also reported in this paper.

Experimental radiative lifetimes for highly excited states and calculated oscillator strengths for lines of astrophysical interest in singly ionized cobalt (Co II)

This work reports new experimental radiative lifetimes and calculated oscillator strengths for transitions of astrophysical interest in singly ionized cobalt. More precisely, 19 radiative lifetimes in Co+ have been measured with the time-resolved laser-induced fluorescence technique using one- and two-step excitations. Out of these, seven belonging to the high lying 3d7(4F)4d configuration in the energy range 90 697-93 738 cm-1 are new, and the other 12 from the 3d7(4F)4p configuration with energies between 45 972 and 49 328 cm-1 are compared with previous measurements. In addition, a relativistic Hartree-Fock model including core-polarization effects has been employed to compute transition rates. Supported by the good agreement between theory and experiment for the lifetimes, new reliable transition probabilities and oscillator strengths have been deduced for 5080 Co ii transitions in the spectral range 114-8744 nm.

Branching fractions and A values in singly ionized tantalum (Ta II)

Aims. We report on the theoretical and experimental lifetimes of Ta II, and calculated branching fractions for selected transitions. Methods. The theoretical data are obtained by means of a relativistic Hartree-Fock method with detailed attention to correlation effects. The experimental lifetimes are measured with the time-resolved, laser-induced, fluorescence technique. Results. The calculated results are in good agreement with both previously known and new experimental lifetimes. New transition probabilities have been deduced for a set of Ta II transitions of astrophysical interest.

Atomic structure calculations and beam-foil observations of La IV

Relativistic Hartree–Fock and multiconfigurational Dirac–Fock calculations of atomic structure and transition rates have been carried out in trebly ionized lanthanum (La3+, Z = 57). The calculations have to cope with configuration interaction effects but also with the very complex situation of the collapse of the 4f wave function. The calculations are compared to experimental data obtained with beam-foil spectroscopy in the extreme ultraviolet, at ion energies that favour the production of the spectrum La IV. Besides lines known from sliding spark discharges, many more lines are observed that have not yet been identified. Time-resolved measurements yield three level lifetimes in La IV that agree roughly with the results of our own calculations.