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

Abstract

The atmospheric degradation of HFC-134a (CF 3 CFH 2 ) proceeds via the formation of CF 3 CFHO radicals. Long path length FTIR environmental chamber techniques were used to study the atmospheric fate of CF 3 CFHO radicals. Two competing reaction pathways were identified for CF 3 CFHO radicals: reaction with O 2, CF 3 CFHO + O 2 → CF 3 C(O)F + HO 2, and decomposition via C−C bond scission, CF 3 CFHO + M → CF 3 + HC(O)F + M. CF 3 CFHO radicals were produced by two different reactions: either via the self-reaction of CF 3 CFHO 2 radicals or via the CF 3 CFHO 2 + NO reaction. It was found that decomposition was much more important when CF 3 CFHO radicals were produced via the CF 3 CFHO 2 + NO reaction than when they were produced via the self-reaction of CF 3 CFHO 2 radicals. We ascribe this observation to the formation of vibrationally excited CF 3 CFHO* radicals in the CF 3 CFHO 2 + NO reaction. Rapid decomposition of CF 3 CFHO* radicals limits the formation of CF 3 C(O)F and hence CF 3 COOH in the atmospheric degradation of HFC-134a. We estimate that the CF 3 COOH 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.