The geometries of the reactant, product, and transition state of the titled reaction were optimized at the UHF, UMP2, and UMP4 levels with the double- and triple-zeta basis sets as well as polarization functions using the energy gradient method. The potential barrier for this reaction was calculated to be 1.68 kcal/mol at the MP-SAC4/6-311G** level. The intrinsic reaction coordinate (IRC) was traced at the UMP2/6-311G** level, and the energy profile along the LRC was refined with the subsequent MP-SAC4/6-311G** calculations. The calculated rate constants at the MP-SAC4/6-311G** level are in good agreement with the experimental values in the temperature range 2000-3000 K.