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 t o the standard Hartree-Fock procedure. Relativistic and electron corre lation corrections are included, and configuration interactions involv ing all reliably established La II electron configurations are conside red. Leading eigenvector percentages for the 5d6d and 5d7s configurati ons are reported here for the first time. Criteria are developed and a pplied for selecting the more reliable calculated oscillator strengths . A set of 70 such values is used to calibrate Monograph 145 intensiti es to produce moderately accurate gf-values. Comparison of an initial two-parameter fit to an equation of the form log(gf) - log(I(145)lambd a(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 systema tically too large by about 0.26. The reason for this discrepancy is no t entirely understood, but it is likely to be due at least in part to the incomplete treatment of core polarization effects in our calculati ons. Modification of the original calibration in the light of the expe rimental 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 Monogr aph 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 fo rmula are in good agreement with published astrophysical log (gf) valu es 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.