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

The static system decomposition kinetics of disilane (, 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 logA1,∞ = 15.75 and E1,∞ = 52,200 cal. These parameters yield AHf0(SiH2)298 = (63.5 − Eb, c) kcal mol,−1 where Eb, 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 – Eb, c to 66.0 - Eb, 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 Eb, c = 0, an average value of ΔHf0(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 + Eb, c) kcal mol−1, in good agreement with theoretical calculations.