Energy level classifications and Breit-Pauli oscillator strengths in neutral tin

Spectroscopic observation of embedded tin impurity is currently being investigated as a potential diagnostic for monitoring the erosion of vessel wall tiles in fusion power plants (Foster et al 2007 J. Nucl. Mater. 363-5 152), requiring accurate estimates of the oscillator strengths (OS) of the neutral and near-neutral lines. In response to this, we have undertaken (to our knowledge) the first extensive Breit-Pauli configuration-interaction (CI) calculation of transitions in Sn I using the atomic structure code CIV3. Our one-electron functions and configuration basis sets have been carefully selected to represent accurately all important valence and core-valence correlation effects. The reassignments of several LS spectroscopic labels based on our ab initio CI coefficients are suggested, highlighting the substantial inconsistencies in the literature. We invoke various internal checks to demonstrate the accuracy of our ab initio results, validating the decision not to apply our customary fine-tuning technique due to extreme CI mixing of multiple CSFs in a number of LSJ-coupled wavefunctions. The highlighted deficiencies in the results of previous theoretical compilations and the significant scatter observed in the OS measurements obtained from independent experimental methods increase the impetus for own CI calculation, which represents a major improvement in accuracy.