Dynamics of H(S-2) plus CH(X-2 Pi) reactions based on a new CH2((X)over-tilde(3)A ") surface via extrapolation to the complete basis set limit

A grid of 5285 ab initio points is utilized to construct a 3D potential energy surface (PES) of the CH2(X A.)3 system. In the calculation procedure, the aug-cc-pVXZ (X.=.Q and 5) basis sets with Davidson correction are employed. The reference wave function for the multi-reference configuration interaction calculations is composed of a full valence complete-active-space selfconsistent field wave function. In order to get a more accurate PES, the complete basis set (CBS) limit proposal and the many-body expansion form are used, with the total root mean square deviation of the final CBS-PES being 0.0349 eV. Based on the accurate CH2(X A.)3 CBS-PES, the stationary points and vibrational energy levels are obtained and examined in detail, which agree well with other theoretical results. Then, utilizing the CBS-PES and quasi-classical trajectory method, the integral cross-sections (ICSs) and rate constants of the H( 2S) + CH(X2P). H2(X S+ g) + C( P)1 3 /CH(X2P) + H( 2S) reactions are calculated. It is found that the present ICSs are in good agreement with other theoretical results, and H2(X S+ g) + C( P)1 3 is the major product channel. For this channel, the rate constants calculated in this work agree well with experimental and other theoretical results in the high-temperature range. It is worth noting that at room temperature, the theoretical results, including the present work, are consistent with each other, but they are all higher (about 7-10 times) than the experimental result, which implies that a new measurement for the rate constant at room temperature is necessary.