The reaction mechanism of CH₂ClO radical with NO was investigated by using B3LYP and MP2 methods with the 6-31＋G(d,p) and 6-311＋＋G(d,p) basis sets, and three reaction channels were found. Geometries of the reactants, intermediates, transition states and products were optimized and IRC calculations were carried out. The calculated results successfully explained the conclusion of Wu’s experimental study. From the view of topological analysis of electron density, the changes of chemical bonds in the reactions were discussed, which will be helpful for the experimental research of the atmospheric chemistry. The “energy transition state” and the “structure transition state” in the reaction have been found. The calculated results revealed the relationship between the reaction enthalpy and the “structure transition re-gion”.

Key words: CH₂ClO radical, reaction mechanism, transition state, topological analysis of electronic density