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 CF3CFHO 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 CF3CFHO* 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.