The ab initio methods are employed to study the decomposition of CF3OH by the HO2, HO2 and water, and, HO2 and HF. The five pre-reactive complexes are found, whose stabilities are computed to be -4.4 to -11.7 kcal/mol at the CCSD(T)//B3LYP/6-311G(d,p) level. The investigation shows that the activated barrier for the unimolecular decomposition of CF3OH is reduced from 45.7 to -0.1 kcal/mol for the cleavage with the HO2 and H2O involved. The calculated kinetics shows that the reaction via TS2 is preferable in the atmosphere. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.