The decomposition kinetics of disilane and the heat of formation of silylene

The static system decomposition kinetics of disilane ( \documentclass{article}\pagestyle{empty}\begin{document}${\rm Si}_{\rm 2} {\rm H}_{\rm 6} \mathop {\longrightarrow}\limits^1 {\rm SiH}_{\rm 2} + {\rm SiH}_{\rm 4}$\end{document} , 538–587 K and 10–500 Torr), are reported. Reaction rate constants are weakly pressure dependent, and best fits of the data are realized with RRKM fall‐off calculations using log A 1,∞ = 15.75 and E 1,∞ = 52,200 cal. These parameters yield AH f 0 (SiH 2 ) 298 = (63.5 − E b, c ) kcal mol, −1 where E b, c is the activation energy for the back reaction at 550 K, M = 1 std state. Five other silylene heat‐of‐formation values (ranging from 63.9 – E b, c to 66.0 ‐ E b, c kcal mol −1 ) are deduced from the reported decomposition kinetics of trisilane and methyldisilane, and from the reported absolute and relative rate constants for silylene insertions into H 2 and SiH 4 . Assuming E b, c = 0, an average value of Δ H f 0 (SiH 2 ) = 64.3 ± 0.3 kcal mol −1 is obtained. Also, a recalculation of the activation energy for silylene insertion into H 2 , based in part on the new disilane decomposition Arrhenius parameters, gives (0.6 + E b, c ) kcal mol −1 , in good agreement with theoretical calculations.