B³\varSigma_u^-–X³\varSigma_g^- transition in selenium dimer: ab initio multireference configuration interaction calculations

Theoretical investigation of low-lying electronic states and B^3\varSigma _\rm u^ - --X^3\varSigma _\rm g^ - transition properties of selenium dimer using size-extensivity singly and doubly excitation multireference configuration interaction theory with nonrelativistic all-electron basis set and relativistic effective core potential plus its split valence basis set is presented in this paper. The spectroscopic constants of ten low-lying \varLambda --S bound states have been obtained and compared with experiments. Spin--orbit calculations for coupling between B^3\varSigma _\rm u^ - sates and repulsive ^1\varPi _\rm u, ^5\varPi _\rm u states have been made to interpret the predissociation mechanisms of the B^3\varSigma _\rm u^ - state. The lifetimes of B^3\varSigma _\rm u^ - (\nu=0\sim 6) have been calculated with scalar relativistic effects included or excluded, respectively, and reasonably agree with experimental values.