The mechanism for the reaction CH2SH with NO2 was investigated at the HL//B3LYP/6-311＋＋G(2df,p) level on single potential energy surface. All stationary points involved in the title reaction were calculated at the B3LYP/6-311＋＋G(2df,p) level. Frequency calculation and intrinsic reaction coordinate (IRC) analysis at the same level were applied to validation of the connection of transition states. The results show that CH2SH＋NO2 system has four dominating reaction channels. Firstly, CH2SH and NO2 take the carbon-to-nitrogen approach forming an adduct HSCH2NO2 (a), followed by C—N bond rupture along with H(1)—O(2) bond formation leading to the major product P1 (CH2S＋trans-HONO). This process with a barrier height of 124.1 kJ•mol－1. HSCH2NO2 (a) can undergo the C—O bond formation along with C—N bond rupture to HSCH2ONO (b), and the barrier height is exceedingly high, 238.34 kJ•mol－1. b will take subsequent conversion and dissociation to products P2 (CH2S＋cis-HONO), P3 (CH2S＋HNO2) and P4 (SCH2OH＋NO). All the channels are exothermic reactions and the reaction energy of generation is －150.37, －148.53, －114.42 and －131.56 kJ•mol－1, respectively. The channel R→a→TSa/P1→P1 is the major channel for the reaction of CH2SH with NO2. Apparent activation energy for the major channel is －91.82 kJ•mol－1. The fitted three-parameter expression for the major channel (R→a→TSa/P1→P1) is kCVT/SCT＝8.3×10－40T4.4exp(12789.3/T) in the temperature range of 200～3000 K, in which k takes unit of cm3•molecule－1•s－1.

Key words: CH₂SH, NO₂, density functional theory (DFT), reaction mechanism, rate constant