AbstractThe gas‐phase decompositions of methylsilane and methylsilane‐d3have been investigated in a single‐pulse shock tube at 4700 torr total pressure in the temperature range of 1125–1250 K. For CH3SiD3at 1200 K three primary steps occur in the homogeneous decomposition with efficiencies in parentheses:\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm CH}_{\rm 3} {\rm SiD}_{\rm 3} \mathop {\longrightarrow} \limits^1 {\rm CH}_{\rm 3} {\rm SiD} + {\rm D}_{\rm 2} \left( {0.71} \right) $$\end{document},\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm CH}_{\rm 3} {\rm SiD}_{\rm 3} \mathop {\longrightarrow} \limits^2 {\rm CH}_{\rm 4} + {\rm SiD}_{\rm 2} \left( {0.15} \right) $$\end{document}, and\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm CH}_{\rm 3} {\rm SiD}_{\rm 3} \mathop {\longrightarrow} \limits^3 {\rm CH}_{\rm 2} \raise1pt\hbox{=\kern-3.45 pt=} {\rm SiD}_{\rm 2} \left( {0.14} \right) $$\end{document}. For CH3SiH3at 1200 K the primary CH4elimination efficiency is 0.09 while the total primary H2elimination efficiency is 0.91. Minor product formations of C2H4, acetylene, dimethylsilane, and SiH4are di