Role of Excited CF₃CFHO Radicals in the Atmospheric Chemistry of HFC-134a

The atmospheric degradation of HFC-134a (CF₃CFH₂) proceeds via the formation of CF₃CFHO radicals. Long path length FTIR environmental chamber techniques were used to study the atmospheric fate of CF₃-CFHO radicals. Two competing reaction pathways were identified for CF₃CFHO radicals: reaction with O₂, CF₃CFHO + O₂ → CF₃C(O)F + HO₂, and decomposition via C-C bond scission, CF₃CFHO + M → CF₃ + HC(O)F + M. CF₃CFHO radicals were produced by two different reactions: either via the self-reaction of CF₃CFHO₂ radicals or via the CF₃CFHO₂ + NO reaction. It was found that decomposition was much more important when CF₃CFHO radicals were produced via the CF₃CFHO₂ + NO reaction than when they were produced via the self-reaction of CF₃CFHO₂ radicals. We ascribe this observation to the formation of vibrationally excited CF₃CFHO* radicals in the CF₃CFHO₂ + NO reaction. Rapid decomposition of CF₃-CFHO* radicals limits the formation of CF₃C(O)F and hence CF₃COOH in the atmospheric degradation of HFC-134a. We estimate that the CF₃COOH yield from atmospheric oxidation of HFC-134a is 7-20%. Vibrationally excited alkoxy radicals may play an important role in the atmospheric chemistry of other organic compounds.