Theoretical study on the kinetics for OH reactions with CH₃OH and C₂H₅OH

Kinetics and mechanisms for reactions of OH with methanol and ethanol have been investigated at the CCSD(T)/6-311 + G(3df, 2p)//MP2/6-31l + G(3df,2p) level of theory. The total and individual rate constants, and product branching ratios for the reactions have been computed in the temperature range 200-3000 K with variational transition state theory by including the effects of multiple reflections above the wells of their pre-reaction complexes, quantum-mechanical tunneling and hindered internal rotations. The predicted results can be represented by the expressions k₁ =4 .65 × 10^-20 × T^2.68 exp(414/T) and k₂ = 9.11 × 10 ^-20 × T^2.58 exp(748/T) cm³ molecule ^-1 s^-1 for the CH₃OH and C₂H ₅OH reactions, respectively. These results are in reasonable agreements with available experimental data except that of OH + C ₂H₅OH in the high temperature range. The former reaction produces 96-89% of the H₂O + CH₂OH products, whereas the latter process produces 98-70% of H₂O + CH₃CHOH and 2-21% of the H₂O + CH₂CH₂OH products in the temperature range computed (200-3000 K).