Ab initio prediction of the barrier height for abstraction of H from CH4 by OH

The reaction CH4+OH→CH3+H2O has been investigated by ab initio molecular orbital theory with a variety of basis sets and levels of correlation. At the highest level of basis set (Dunning’s correlation consistent) and highest level of correlation [QCISD(T)], the value of ΔH(0) is −13.44 kcal/mol and the classical barrier height is 6.62 kcal/mol which is reduced to 5.24 kcal/mol if zero point effects are included. Transition state theory is used to predict the rate constants and good agreement with the experimental values is found over a broad temperature range.