ABINITIO 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 c orrelation. At the highest level of basis set (Dunning's correlation c onsistent) and highest level of correlation [QCISD(T)], the value of D ELTAH(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 i ncluded. Transition state theory is used to predict the rate constants and good agreement with the experimental values is found over a broad temperature range.