Theoretical investigation on the mechanism and thermal rate constants for the reaction of atomic O (3P) with CHF2Cl

The hydrogen abstraction reaction of atomic O (P-3) with CHF2Cl has been studied theoretically for the first time using ab initio molecular orbital theory. Two nearly degenerate saddle points of (3)A" and (3)A' symmetries have been located for this hydrogen abstraction reaction from the C-H bond. The potential energy surface information has been obtained at the MP2 level with the 6-311G(2d,p) basis set. Energies along the minimum energy path have been improved by a series of single-point ab initio QCISD(T)//MP2 calculation. Changes of geometries, generalized normal-mode vibrational frequencies, and potential energies along the reaction path are discussed. The kinetics nature is obtained using canonical variational transition state theory (CVT) with the small-curvature tunneling (SCT) correction method over a wide temperature range of 200similar to3000 K. The result shows that the variational effect is small, and in the lower-temperature range, the SCT effect is important for the title reaction. The calculated CVT/SCT rate constants exhibit typical non-Arrhenius behavior, and a three-parameter rate-temperature formula is fitted as follows (in units of cm(3) molecule(-1) s(-1)): k(T) = 4.75 x 10(-18)T(2.26) exp(-4318.02/T). The calculated rate constants are compared with the available experimental values.