Relative rate constants for reactions of HFC 152a, 143, 143a, 134a, and HCFC 124 with F or Cl atoms and for CF 2 CH 3 , CF 2 HCH 2 , and CF 3 CFH radicals with F 2 , Cl 2 , and O 2

Relative rate experiments using UV photolysis of F 2 or Cl 2 have been used to determine rate constant ratios for several hydrofluorocarbon (HFC) reactions with Cl or F atoms and for HFC alkyl radicals with molecular halogens. For mixtures with F 2 present, dark reactions are, also, observed which are attributed to thermal dissociation of the F 2 to form F atoms. At 296 K, the rate of reaction (1a) [CF 2 HCH 3 + F → CF 2 CH 3 + HF] relative to (1b) [CF 2 HCH 3 + F → CF 2 HCH 2 + HF] is k 1a / k 1b = 0.73 (±0.13) and is independent of T (= 262–348 K). At 296 K, the ratio of reaction (2a) [CF 2 HCH 2 F + F → products] to that of ( k 1a + k 1b ) is ( k 1a + k 1b )/ k 2a = 2.7 (±0.4), and for reaction (2b) [CF 3 CH 3 + F → products] ( k 1a + k 1b )/ k 2b = 22 ± 12. The temperature dependence (263–365 K) of the rate constant of reaction (3) [CF 3 CFH 2 + Cl → products] relative to reaction (4) [CF 3 CFClH + Cl → products] is k 3 / k 4 (±10%) = 1.55 exp(−300 K / T ). For the alkyl radicals formed from HFC 152a (CF 2 HCH 2 and CF 2 CH 3 ) and from HFC 134a (CF 3 CFH), rate constants for the reactions with F 2 and Cl 2 were measured relative to their reactions with O 2 . The rate constant of reaction (5cl) [CF 2 CH 3 + Cl 2 → CF 2 ClCH 3 + Cl] relative to (5o) [CF 2 CH 3 + O 2 → CF 2 (O 2 )CH 3 ] is k 5cl / k 5o (±15%) = 0.3 exp(200 K / T ). For reaction (5f) [CF 2 CH 3 + F 2 → CF 3 CH 3 + F], k 5f / k 5o (±35%) = 0.23. The ratio for reaction (6f) [CF 2 HCH 2 + F 2 → CF 2 HCH 2 F + F] relative to (6o) [CF 2 HCH 2 + O 2 → CF 2 HCH 2 O 2 ] is k 6f / k 6o (±40%) = 1.23 exp(−730 K / T ). The rate constant ratio for reaction (8cl) [CF 3 CFH + Cl 2 → CF 3 CFClH + Cl] relative to reaction (8o) [CF 3 CFH + O 2 → CF 3 CFHO 2 ] is k 8cl / k 8o (±18%) = 0.16 exp(−940 K / T ). For reaction (8f) [CF 3 CFH + F 2 → CF 3 CF 2 H + F], k 8f / k 8o (±35%) = 0.6 exp(−860 K / T ). © 1993 John Wiley & Sons, Inc.