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 + H2O (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. [ABSTRACT FROM AUTHOR]