Theoretical investigation of the reaction mechanisms and kinetics of CFCl2CH2O2and ClO in the atmosphere

The reaction between CFCl(2)CH(2)O(2)radicals and ClO was studied using the B3LYP and CCSD(T) methods associated with the 6-311++G(d,p) and cc-pVTZ basis sets, and subsequently RRKM-TST theory was used to predict the thermal rate constants and product distributions. On the singlet PES, the dominant reaction is the addition of the ClO oxygen atom to the terminal-O of CFCl(2)CH(2)O(2)to generate adduct IM1 (CFCl2CH2OOOCl), and then dissociation to final productsP1(CFCl2CHO + HO2+ Cl) occurs. RRKM theory is employed to calculate the overall and individual rate constants over a wide range of temperatures and pressures. It is predicted that the collision-stabilizedIM1(CFCl2CH2OOOCl) dominates the reaction at 200-500 K (accounting for about 60-100%) and the dominant products areP1(CFCl2CHO + HO2+ Cl). The yields of the other products are very low and insignificant for the title reaction. The total rate constants exhibit typical "falloff" behavior. The pathways on the triplet PES are less competitive than that on the singlet PES. The calculated overall rate constants are in good agreement with the experimental data. The atmospheric lifetime of CFCl(2)CH(2)O(2)in ClO is around 2.04 h. TD-DFT calculations imply thatIM1(CFCl2CH2OOOCl),IM2(CFCl2CH2OOClO) andIM3(CFCl2CH2OClO2) will photolyze under sunlight.