KINETICS OF THE SIH3-2 REACTION - A NEW TRANSITION-STATE FOR SIO PRODUCTION(O)

The mechanism of SiO formation in the laser photolysis of SiH4/O-2/CCl 4 mixtures was investigated using a laser-induced fluorescence method. Measured rates for the SiO production corresponded to the decay rates of SiH3 radical and depended linearly on the O-2 concentration. The y ield of SiO was estimated on the basis of LIF intensity, and it was fo und that SiO was one of the major products in the SiH3 + O-2 reaction. The bimolecular rate constant for the SiO production was determined t o be (1.14 +/- 0.18) x 10(-11) cm(3) molecules(-1) s(-1). Ab initio mo lecular orbital calculations were performed for various pathways of th e SiH3 + O-2 reaction. Geometries were optimized at the MP2(full)/6-31 G(d) level of theory, and relative energies and barrier heights were c alculated at the G2(MP2) level of theory. Silyl radical and O-2 react to form SiH3OO, which irreversibly decomposes to various excited produ cts. A new transition state fur the production of cyclic H2SiO2 (silad ioxirane) + H from SiH3OO adduct was found. Possible decomposition cha nnels of the vibrationally excited products of the SiH3 + O-2 reaction to produce SiO are discussed.