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 logA_1,∞ = 15.75 and E_1,∞ = 52,200 cal. These parameters yield AH_f⁰(SiH₂)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 H₂ and SiH₄. Assuming E_{b, c} = 0, an average value of ΔH_f⁰(SiH₂) = 64.3 ± 0.3 kcal mol^?1 is obtained. Also, a recalculation of the activation energy for silylene insertion into H₂, 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.