Quantum chemistry UMP2 method was performed to study the reaction mechanism of the reactions of CH_2X (X= H, F, Cl) with O_3. The geometric configurations of reactants, intermediates, transition states and products were optimized by UMP2 method at 6-311+ + G~(* *) level and the energies of stationary points along the pathways were calculated at UQCISD(t)/6-311 + + G~(* *) level. Intermediates and transition states were confirmed by vibration analysis. From the results of the reaction mechanism of the reactions of CH_2X (X = H, F, Cl) with O_3, one can see tlaat they are active radicals depleting ozone and the order of activity is CH_2F > CH_3 > CH_2C1. That is to say, CH2F is the most active chemical of the three radicals depleting the ozone layer. It is also found that the reactions of CH_2X (X= H, F, Cl) with O_3 are strongly exothermic.

Key words: OZONE, REACTION MECHANISM, ACTIVATION ENERGY, HALOHYDROCARBON, METHANE P, FREE RADICAL