Abstract: Absolute rate constant for the reaction of CCl2 radical with H2O is obtained as (5.45±0.95)×10－14 cm3•molecule－1•s－1 by LPLIF technique. The CCl2 is first produced by 213 nm laser photolysis of CCl4. The mechanism for the reaction CCl2＋H2O has been studied using a highlevel ab initio G2MP2 method. It is found that there are two reaction mechanisms: insertion and additionelimination. The three primary product channels, HCl＋HClCO， HCl＋transClCOH and HCl＋cisClCOH, are studied in detail. Moreover, the branch ratios are calculated using RRKMTST and convention transition state theories. The calculations show that at lower temperatures the major product channel is HCl＋HCClO via the insretion of C atom of CCl2 into OH bond of H2O, whereas the formation of HCl＋transClCOH dominates at higher temperatures.

Key words: CCl2 radical, Rate constant, Ab initio theoretical calculation,