Theoretical study on the reaction mechanisms of CH2SHÂ +Â NO reaction

The mechanisms for the CH2SH + NO reaction were investigated on both of the singlet and triplet PES at the BMC-CCSD//B3LYP/6-311+G(d,p) level. The results indicate that the singlet PES is much lower than the triplet PES energetically; therefore, the reaction occurs on the singlet PES dominantly. The most favorable channel on the singlet PES takes place by a barrierless addition of N atom to CH2SH radical to form HSCH2NO. Subsequently, the rearrangement of the initial adduct HSCH2NO (IM1) to form another intermediate IM3 via a four-center transition state, followed by the C-O bond fission in IM3 leading to the major product CH2S + HNO. Due to high barriers, other product including HC(N)SH + HO, HON + CH2S, and HNO + CHSH could be negligible. The direct abstraction channel was also determined to yield CH2S + HON. With high barrier (33.3 kcal/mol), it is not competitive with the addition channel, in which all stationary points are lower than reactant energetically. While on the triplet PES, with the lowest barrier height (18.8 kcal/mol), the direct N-abstracted channel to form CH2S + HNO is dominant. However, it is not competitive with the channels on the singlet PES. Our results are in good accordance with experimental conclusions that the reaction proceeds via addition mechanism.