Silylene does react with carbon monoxide: Some gas-phase kinetic and theoretical studies

Time-resolved studies of the reaction of silylene, SiH2, with CO have been carried out over the pressure range 10-500 Torr (with SF6 as bath gas) at four temperatures in the range 299-477 K, using laser flash photolysis to generate and monitor SiH2. The second-order rate constants obtained were pressure dependent, indicating that the reaction is a third-body assisted association process close to its third-order limit. The second-order rate constants at a pressure of 100 Torr gave the following Arrhenius parameters: log(A/cm(3) molecule(-1) s(-1)) = -13.92 +/- 0.23, E-a = -13.02 +/- 1.62 kJ mol(-1), where the uncertainties are single standard deviations. Ab initio calculations at the G2 level indicated formation of silaketene, H2SiCO, as the initial product. RRKM theoretical calculations, employing a variational transition state based on the ab initio surface, fitted the kinetic data very well with a dissociation enthalpy, H(D)degrees (H2Si-CO) = 89 kJ mol(-1), in very good agreement with ab initio calculation. These studies show unequivocally that SiH2 does react rapidly with CO and that an earlier gas-phase investigation was carried out under conditions unfavorable for the observation of reaction.