AB-INITIO PREDICTIONS OF THE LOWEST ELECTRONIC STATES, STRUCTURES VIBRATIONAL FREQUENCIES OF PHENYLPHOSPHINIDENE

The singlet-triplet energy splitting of phenylphosphinidene is predict ed to be -21 kcal/mol at the Davidson corrected TC-CISD/6-31G//CISD/6 -31G level of theory. The Delta E(S-T) of phenylphosphinidene is the same as that of phenylnitrene, which also has a triplet ground state. The open-shell singlet and closed shell singlet states reverse their o rder when the group 15 element is changed from N to P. Comparisons bet ween NR and PR (R = H, methyl and phenyl) show that the phenyl group s trongly stabilizes the S-0 state of phenylnitrene whereas there is no significant change in Delta E(S-T) for phenylphosphinidene. Methyl sub stitution leaves Delta E(S-T) unchanged for both nitrene and phosphini dene.