Theoretical Investigation of the O(3P) + CHX2 (X = F, Cl) Reactions

The reactions of oxygen atoms with the CHX 2 (X = F, Cl) radicals have been studied for the first time using the G2(MP2) method. The extensive calculations reveal the capture-limited association−elimination mechanism for the O + CHX 2 reaction. For the O( 3 P) + CHF 2 reaction, two energy-rich intermediates, CHF 2 O* and CF 2 OH*, are formed along the reaction path. CHF 2 O* has four unimolecular production channels: H + CF 2 O; CF 2 OH; F + CHFO; and HF + FCO. The isomer CF 2 OH can decompose to H + CF 2 O, HF + FCO, OH + CF 2, and F + FCOH. The analogous production channels such as Cl + CHClO, H + CCl 2 O, HCl + ClCO, OH + CCl 2, and Cl + ClCOH are investigated for the O( 3 P) + CHCl 2 reaction. It should be noted that three-center direct elimination of HCl from the adduct CHCl 2 O* was characterized using the semiempirical AM1 method. On the basis of the ab initio potential energy surfaces, the kinetics and the dynamics for these two atom/radical reactions are discussed qualitatively. For the O + CHF 2 reaction, H and CF 2 O are predicted to be the major products. For the O( 3 P) + CHCl 2 reaction, the major production channel is the formation of Cl + CHClO, while the HCl + ClCO channel may be competitive.