Accurate configuration-interaction calculation of transitions in Sn II

A large-scale Breit-Pauli configuration-interaction calculation has been undertaken of all possible 85 E1 optically allowed and intersystem transitions in Sn II among the 22 energetically lowest-lying levels. We have presented a discussion of a sequence of increasingly complex calculations, performed in the LS coupling scheme, in which we have satisfied the necessary criterion in order that we could be confident that a satisfactory convergence of all important valence and core-valence correlation effects had been attained. Judging by the extensive checks we have subjected our results to, we estimate realistic uncertainties in the region of 5% for the stronger transitions studied, achieving an accuracy required for the proposed applications in astrophysical and fusion research. It is encouraging that we can propose possible deficiencies in the theoretical models of previous calculations in an attempt to account for disparities with present data. Although the observed consistency between our results and the greater part of experimental measurements is a comforting indication of reliability, the analysis is not without its discrepancies. We would argue, however, that the present work, representing the most accurate data available to date, warrants further elaborate experimental study. Our calculated fine-tuned oscillator strength for the astrophysically important transition at 1400.5 A fl = 1.205 ± 0.060 puts into question the conclusions of Sofia et al (Sofia U J, Meyer D M and Cardelli J A 1999 Astrophys. J. 522 L137) that they measured gas-phase ratios of Sn/H in the interstellar medium that appear to be supersolar.