The mechanism of the reaction of the singlet CCl2 with O3 has been studied by using ab initio method at 6-31G(d) level. The geometries of the reactants, intermediate, transition state and products of the reaction have been optimized with the gradient technique. The single point energy calculations of the species have been performed by MP2/6-31G(d) method. The relative structure data of the reactants, intermediate, transition state and products are given. The mechanism proposed here is that the reactant molecules combine with each other first to form an energy-enriched intermediate, followed by decomposition of the intermediate to give CCl2O and O2. The reaction is exothermic by 516.88kJ.mol^-^1[MP2/6-31G(d)//HF/6-31G(d)]. The potential energy profile along reaction path has been obtained through IRC calculations.

Key words: OZONE, REACTION MECHANISM, SINGLET, AB INITIO CALCULATION