Reaction of a fluorine atom with methanol: potential energy surface considerations.

There are several experimental studies of the F + CH3OH reaction but very little in the way of reliable theory. Here reported are aug-cc-pVQZ CCSD(T) computations for two different reaction pathways. The more exothermic pathway B, which produces methylhydroxy radical (ΔE= -37.7 kcal mol(-1)), has a van der Waals minimum as the entrance complex and a transition state lying 0.15 kcal mol(-1) below F + CH3OH. The exit complex B is bound by 5.0 kcal mol(-1) relative to separated HF + CH2OH. Although pathway A, which produces the methoxy radical, is 9.3 kcal mol(-1) less exothermic than B, A has a deep entrance complex, 6.6 kcal mol(-1) below reactants. Also, transition state A lies 4.1 kcal mol(-1) below separated F + CH3OH. The latter two energetic features nicely explain why 40% of the laboratory products follow the less exothermic pathway A.