The kinetics and mechanism of the shock induced gas phase decomposition of ethylsilane

The decomposition kinetics of ethylsilane under shock tube conditions (P_T ca. 3100 torr, T ? 1080–1245 K), both in the absence and presence of silylene trapping agents (butadiene and acetylene) are reported. Arrhenius parameters under maximum butadiene inhibition are: log k(C₂H₅SiH₃) = 15.14-64,769 ± 1433 cal/2.303 RT; log k(C₂H₅SiD₃) = 15.29-66,206 ± 1414/2.303 RT. The uninhibited reaction is subject to silylene induced decomposition (63% lowest T -- 24% highest T). Major reaction products are ethylene and hydrogen, consistent with two dominant primary dissociation reactions: C₂H₅SiD₃ → C₂H₅SiD + D₂, ? ? 0.66; C₂H₅SiD₃ → CH₃CH = SiD₂ + HD, ? ? 0.30. Minor products suggest several other less important primary processes: alkane elimination, ? ?0.02, and free-radical production via simple bond fission, ? ?0.02. An upper limit for the activation energy of the decomposition, C₂H₅SiH → C₂H₄ + SiH₂, of E < 30 ± 4 kcal is established, and speculations on the mechanism of this decomposition (concerted or stepwise) with conclusions in favor of the stepwise path are made. Computer modeling studies for the reaction both in the absence and presence of butadiene are shown to be in good agreement with the experimental observations.