Multireference configuration interaction and second-order perturbation theory calculations for the 1 3A″, 1 1A″, and 1 1A′ electronic states of vinylnitrene and vinylphosphinidene

MRCI and CASPT2 calculations from a (4, 4) MCSCF active space predict both vinylnitrene and vinylphosphinidene to have 3A″ ground states. For vinylnitrene, the lowest open-shell singlet (1A″) and closed-shell singlet (1A′) states lie 15 and 40 kcal/mol higher in energy, respectively. The corresponding relative singlet energies in vinylphosphinidene are 17 and 23 kcal/mol, respectively. The reduced separation between the singlet states in H2CCHP compared to H2CCHN is attributed to decreased conjugation between the double bond and the pnictogen atom in the phosphinidene.