Theoretical studies on the reactions of hydroxyl radicals with trimethylsilane and tetramethylsilane

The multiple-channel reactions OH + SiH(CH₃)₃ → products (R1) and the single-channel reaction OH + Si(CH₃) ₄ → Si(CH₃)₃CH₂ + H ₂O (R2) have been studied by means of the direct dynamics method at the BMC-CCSD//MP2/6-311+G(2d,2p) level. The optimized geometries, frequencies and minimum energy path are all obtained at the MP2/6-311+G(2d,2p) levels, and energy information is further refined by the BMC-CCSD (single-point) level. The rate constants for every reaction channels are calculated by canonical variational transition states theory (CVT) with small-curvature tunneling (SCT) contributions over the temperature range 200-2,000 K. The theoretical total rate constants are in good agreement with the available experimental data, and the three-parameter expression k ₁ = 2.53×10^-21 T ^3.14 exp(1, 352.86/T), k ₂ = 6.00 × 10^-19 T ^2.54 exp(-106.11/T) (in unit of cm³ molecule ^-1 s^-1) over the temperature range 200-2,000 K are given. Our calculations indicate that at the low temperature range, for reaction R1, H-abstraction is favored for the SiH group, while the abstraction from the CH₃ group is a minor channel.