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

Abstract

The mechanism of SiO formation in the laser photolysis of SiH4/O2/CCl4 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 O2 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 SiH3 + O2 reaction. The bimolecular rate constant for the SiO production was determined to be (1.14 ± 0.18) × 10-11 cm3 molecules-1 s-1. Ab initio molecular orbital calculations were performed for various pathways of the SiH3 + O2 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 O2 react to form SiH3OO, which irreversibly decomposes to various excited products. A new transition state for the production of cyclic H2SiO2 (siladioxirane) + H from SiH3OO adduct was found. Possible decomposition channels of the vibrationally excited products of the SiH3 + O2 reaction to produce SiO are discussed.