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

The reactions of H with SiH3F, SiH2F2 and SiHF3 and have been studied syste matically using the direct dynamics method for the first time. A direct hyd rogen abstraction mechanism has been revealed. The geometries of reactants, products and transition states have been optimized at the UMP2 level. Sing le-point calculations have been carried out at the G2MP2 level of theory. B ased on the ab initio data, the rate constants have been calculated using t he canonical variational transition state theory with the small-curvature t unneling correction method (CVT/SCT) over a wide temperature range of 200-3 000 K. The CVT/SCT rate constants exhibit typical non-Arrhenius behavior. T hree-parameter rate-temperature formulas are fitted as follows : k(1) (T) = (1.81 x 10(-19))T-2.85 exp(-694.74 T) for the reaction of H with SiH3F, k( 2)(T) = (1.43 x 10(-20))T-3.19 exp(-1102.60/T) for the reaction of H with S iH2F2, k(3)(T) = (2.34 x 10(-20))T-2.87 exp(-2002.20/T) for the reaction of H with SiHF3, in units of cm(3) molecule(-1) s(-1). The theoretical result s are in good agreement with the available experimental data. The fluorine substitution decreases the reactivity of the Si-H bond.