THE PRIMARY STEPS IN THE PHOTOCHEMISTRY OF W(CO)5L - SUBPICOSECOND PHOTOCHEMISTRY

The ligand substitution photochemistry of [W(CO)5L] (L = py,pip) exhibits higher quantum yields in the singlet region than the triplet region. Across the lowest singlet, yields are higher for 1E than 1A components. [W(CO)5S] (S = solvent) forms in less than 20 ps on 355 nm excitation. The primary products observed at 50 ps vary as a function of both leaving group, L, and entering group, S. Solvent effects are consistent with a key role for vibrational relaxation of [W(CO)5S] on the ground state surface. Heller theory can account for the relative reactivity of triplets, but it is seen that an account of the singlets must exploit more than has yet been brought to bear. Hollebone's octet rule is promising, implying limited utility for Born-Oppenheimer and Franck-Condon Approximations.