gf-values for singly ionized lanthanum based on a new calibration of NBS Monograph 145 intensities

Oscillator strengths and transition probabilities for Lan are computed using a Hartree-plus-statistical-exchange-interaction approximation to the standard Hartree-Fock procedure. Relativistic and electron correlation corrections are included, and configuration interactions involving all reliably established La II electron configurations are considered. Leading eigenvector percentages for the 5d6d and 5d7s configurations are reported here for the first time. Criteria are developed and applied for selecting the more reliable calculated oscillator strengths. A set of 70 such values is used to calibrate Monograph 145 intensities to produce moderately accurate gf-values. Comparison of an initial two-parameter fit to an equation of the form log(gf) - log(I(145)lambda(3)) = c(1) + c(2) E(upper) (for E(upper) in cm(-1)) with beam-laser lifetime measurements shows the resulting log(gf) values to be systematically too large by about 0.26. The reason for this discrepancy is not entirely understood, but it is likely to be due at least in part to the incomplete treatment of core polarization effects in our calculations. Modification of the original calibration in the light of the experimental lifetime data yields the following recommended values for the fitting parameters: c(1) = - 16.503 and c(2) = 7.752 x 10(-5). Log(gf) values computed for La II lines using this calibration of the Monograph 145 intensities should be accurate to about +/- 0.20 dex over the energy range 0 to similar to 70 000 cm(-1). The predictions of this formula are in good agreement with published astrophysical log (gf) values for 34 La II features in the solar spectrum longward of similar to 4300 Angstrom, and yield a mean difference (and standard deviation) of - 0.07 +/- 0.30.