KINETICS AND MECHANISM OF THE REACTIONS OF O(P-3) WITH SIH4, CH3SIH3, (CH3)2SIH2, AND (CH3)3SIH

The reactions of O(3P) atoms with the silanes Me(4-n)SiH(n) (n = 1-4) have been investigated at room temperature in a discharge flow system with mass spectrometric detection and also in stationary photolysis experiments. Analysis of the end products provided conclusive evidence that the only primary process occurring in each case was the abstraction of hydrogen from the Si-H bond by the O atom leading to the formation of the OH and silyl radicals. The values of the rate constants obtained are k/10(-13) cm3 s-1): k(O + SiH4) = 3.5, k(O + SiD4) = 1.4, k(O + MeSiH3) = 8.9; k(O + Me2SiH2) = 18.0 k(O + Me3SiH) = 30.6, and k(O + Me3SiD) = 16.0. The marked increase in rate constant with methylation is unexpected in view of the known similarity of the Si-H bond dissociation energy in SiH4 and the methylsilanes. A possible explanation is offered in terms of a reaction model involving partial charge transfer from Si to the attacking O, followed by proton transfer.