The gas-phase decomposition of methylsilane. Part II. Mechanisms of decomposition under static system conditions

The static system pyrolysis of methylsilane (T ～ 700 K, P_T ～ 150 torr), pure and in the presence of ethylene, propylene, and acetylene, has been investigated. It is proposed that in the uninhibited system, the major products (silane and dimethylsilane) are produced by free radical processes, and that the free radicals are formed at the walls from methylsilylenes. In the presence of olefins, the free radicals are trapped to form methylsilane adducts. In acetylene, trapping of methylsilylenes prevents free radical production and eliminates the free radical produced products of the pure and the olefin inhibited systems. Rates of initiation correlate with rates of reactant loss in acetylene inhibited systems, and with rates of hydrogen formation in olefin inhibited systems. Rough estimates of primary dissociation process yields give for the 1,1-H₂ elimination ?_1,1 ? 0.78, for the 1,2-H elimination ?_1,2 ? 0.16, and for the methane elimination ?CH₄ ? 0.06 at 700 K. Deuteration lowers initial step kinetics by about 15%.