THEORETICAL-STUDY OF THE KINETICS OF THE HYDROGEN ABSTRACTION FROM METHANOL - 1 - REACTION OF METHANOL WITH FLUORINE-ATOMS

Ab initio calculations at different levels of theory and using several basis sets were performed for the title two-channel hydrogen-abstract ion reaction. Conclusions are drawn from G2 energies. These calculatio ns have shown that this reaction, which can give two products (namely, CH3O and CH2OH), proceeds through the formation of intermediate compl exes followed by transition states with quite negligible activation en ergy. We propose a method for the calculation of the rate constant of a bimolecular reaction proceeding through the formation of two interme diate complexes. General equations, taking into account the rotational energy, are derived from RRKM theory, using the simplified version of the SACM theory. The resulting calculated overall rate constant as we ll as the yield of the methoxy branching ratio are in very good agreem ent with experimental findings. The expressions for the site-specific rate constants k(CH3O) and k(CH2OH) allow the description of the react ion kinetics over a wide range of temperatures. A temperature rate con stant fit, convenient for chemical modeling studies, is k(CH3O) = 1.0 x 10(-10) (T/300)(0.5) cm(3) molecule(-1) s(-1) and k(CH2OH)= 6.9 x 10 (-11) (T/300)(0.27) cm(3) molecule(-1) s(-1).