Kinetics of the gas-phase reaction between iodine and monosilane and the bond dissociation energy D(H3Si?H)

The title reaction has been investigated in the temperature range of 494–545 K. During the early stages of reaction the only observed products were silyl iodide and hydrogen iodide. Initial rates were found to obey the rate law over a wide range of initial iodine and monosilane pressures. Secondary reactions, most probably of SiH₃I with I₂, became more important as the reaction progressed. However, provided SiH₄]₀/I₂]₀ > 20, these secondary processes had a negligible effect on the kinetics, and an integrated rate expression could be used. These kinetics are consistent with an iodine atom abstraction chain mechanism, and for the step has been deduced. From this the bond dissociation energy D(SiH₃? H) = 378 ± 5 kJ/mol (90 kcal/mol) is obtained. The kinetic and thermochemical implications of this value, especially to the pyrolysis of monosilane, are discussed.