Kinetics of the SiH₃ + O₂ Reaction:  A New Transition State for SiO Production

The mechanism of SiO formation in the laser photolysis of SiH 4 /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 SiH 3 radical and depended linearly on the O 2 concentration. The yield of SiO was estimated on the basis of LIF intensity, and it was found that SiO was one of the major products in the SiH 3 + O 2 reaction. The bimolecular rate constant for the SiO production was determined to be (1.14 ± 0.18) × 10 -11 cm 3 molecules -1 s -1 . Ab initio molecular orbital calculations were performed for various pathways of the SiH 3 + O 2 reaction. Geometries were optimized at the MP2(full)/6-31G(d) level of theory, and relative energies and barrier heights were calculated at the G2(MP2) level of theory. Silyl radical and O 2 react to form SiH 3 OO, which irreversibly decomposes to various excited products. A new transition state for the production of cyclic H 2 SiO 2 (siladioxirane) + H from SiH 3 OO adduct was found. Possible decomposition channels of the vibrationally excited products of the SiH 3 + O 2 reaction to produce SiO are discussed.