Theoretical study on the reactions of CF/CCl with O2

The reaction mechanisms of CF and CCl with O-2 have been investigated theoretically on the doublet potential energy surfaces (PESs). The QCISD/6-311++G(d,p) single-point calculations are performed using the B3LYP/6-311++G(d,p) optimized geometries to accurately determine the energetics. The two product channels, F + CO2 and FCO + O, have been found in the CF + O-2 reaction. The former is more competitive because the formation pathway of it undergoes fewer reaction steps and lower barriers than that of FCO + O. In the case of the CCl + O-2 reaction, the two similar channels of Cl + CO2 and ClCO + O have also been identified, and the first is less preferable. The title reactions in question are of practical significance in high-temperature processes, because the initial associations are barrier-present. This paper also discusses the effects of halogenations on the reactivity, the reaction pathways, the product channels and the reaction enthalpies of the three CX + O-2 reactions (X = H, F or Cl). The reactivity of CX + O-2 decreases in the order of CH, CF and CCl. (c) 2009 Elsevier B.V. All rights reserved.