Ab initio and kinetic calculations for the reactions of H with SiH(4−n)Fn (n = 1–3)

Abstract

The reactions of H with SiH₃F, SiH₂F₂ and SiHF₃ have been studied systematically using the direct dynamics method for the first time. A direct hydrogen abstraction mechanism has been revealed. The geometries of reactants, products and transition states have been optimized at the UMP2 level. Single-point calculations have been carried out at the G2MP2 level of theory. Based on the ab initio data, the rate constants have been calculated using the canonical variational transition state theory with the small-curvature tunneling correction method (CVT/SCT) over a wide temperature range of 200–3000 K. The CVT/SCT rate constants exhibit typical non-Arrhenius behavior. Three-parameter rate–temperature formulas are fitted as follows: k₁(T) = (1.81 × 10⁻¹⁹)T^2.85 exp(−694.74/T) for the reaction of H with SiH₃F, k₂(T) = (1.43 × 10⁻²⁰)T^3.19 exp(−1102.60/T) for the reaction of H with SiH₂F₂, k₃(T) = (2.34 × 10⁻²⁰)T^2.87 exp(−2002.20/T) for the reaction of H with SiHF₃, in units of cm³ molecule⁻¹ s⁻¹. The theoretical results are in good agreement with the available experimental data. The fluorine substitution decreases the reactivity of the Si–H bond.