Theoretical study of bending and symmetric stretching vibrational levels of the lowest five quintet and two triplet states of FeH2

Adiabatic potential surfaces of the lowest two triplet states and the lowest five quintet states of FeH2 were calculated using ab initio multi-reference singly and doubly excited configuration interaction plus Davidsonʹs type correction. Multi-reference coupled pair approximation was applied to obtain more accurate term energies of the triplet states. In contrast to the quintet states, which are known to be linear, the lowest two triplet states are strongly bent. Vibrational analyses of both quintet and triplet states were carried out. We discuss the effect of non-adiabatic coupling on the bending vibrational levels of 5B2 and (2)5A1 through a conical intersection.