DYNAMICS OF PHOTOCHEMICAL-REACTIONS - SIMULATION BY QUANTUM CALCULATIONS FOR TRANSITION-METAL HYDRIDES

The photodissociation dynamics of some organometallic molecules in the lowest repulsive electronically states are reported for the following concurrent primary reactions: (i) the homolysis of a metal-hydrogen bond vs. the heterolytic loss of a carbonyl ligand in HCo(CO)4; (ii) the photoinduced elimination of molecular hydrogen vs. the loss of a carbonyl ligand in H2Fe(CO)4; and (iii) the photoinduced elimination of molecular hydrogen vs. the loss of a mesithylene ligand in H2Os(CO)Mes (Mes = C6H3(CH3))3. The dynamics are simulated quantum mechanically using a time-dependent wavepacket propagation technique on potential energy surfaces obtained from CASSCF/CCI calculations for HCo(CO)4 and H2Fe(CO)4 and from SCF-INO/MRCI calculations for H2Os(CO)Mes. This approach gives a rather detailed view of some important elementary processes that contribute to the photochemistry of these complexes. The nature of the photoactive excited states is determined without ambiguity, as well as the time scales, the branching ratio of the different primary dissociation pathways, and some features of the absorption spectra. (C) 1994 John Wiley & Sons, Inc.