Two possible reaction channels for the reaction of CH₂SH＋Cl have been studied at the MP2(Full)/6-311G(d,p) and B3LYP/6-311G(d,p) levels. Geometries of the reactants, intermediates, transition states and products were optimized and IRC calculations were carried out. The computed results show that the reaction proceeds through the addition of a Cl atom to CH₂SH by either Cl—C or Cl—S combination to form initial intermediates. The cleavage and formation of the chemical bonds in the reaction pathways have been discussed by the topological analysis of electronic density. The “energy transition state” and the “structure transition state” in both channels of the studied reaction have been found. The calculated results suggest the relationship between the reaction enthalpy and the “structure transition region”.

Key words: radical reaction, energy transition state, structure transition state, structure transition region, topological analysis of electronic density