The electronic states of SeF: A reinterpretation of the chemiluminescent emission of the reaction of selenium with fluorine

The low-lying doublet and quartet electronic states of the species SeF correlating with the first dissociation channel are investigated theoretically at a high-level of electronic correlation treatment, namely, the complete active space self-consistent field/multireference single and double excitations configuration interaction (CASSCF/MRSDCI) using a quintuple-zeta quality basis set including a relativistic effective core potential for the selenium atom. Potential energy curves for ( Λ + S ) states and the corresponding spectroscopic properties are derived that allows for an unambiguous assignment of the only spectrum known experimentally as due to a spin-forbidden X Π 2 − a ∑ 4 − transition, and not a A Π 2 − X Π 2 transition as assumed so far. For the bound excited doublets, yet unknown experimentally, this study is the first theoretical characterization of their spectroscopic properties. Also the spin-orbit coupling constant function for the X Π 2 state is derived as well as the spin-orbit coupling matrix element between the X Π 2 and a ∑ 4 − states. Dipole moment functions and vibrationally averaged dipole moments show SeF to be a very polar species. An overview of the lowest-lying spin-orbit ( Ω ) states completes this description.