Atmospheric Chemistry of HFC-134a: Kinetic and Mechanistic Study of the CF3CFHO2 + HO2 Reaction

Article abstract of DOI:10.1021/j100087a025

Rate constant measurements for the title reaction and for F + CF3CFH2 are reported over the 210-363 K temperature range.Reacting mixtures of CF3CFHO2 and HO2 radicals are created by the flash photolysis of F2 in the presence of HFC-134a (CF3CFH2), H2, and O2 and are probed by time-resolved UV absorption spectroscopy.The deconvolution of spectra taken at various delay times provides concentration versus time profiles for the respective radical species.A comparison of the initial CF3CFHO2 and HO2 concentrations yields a relative rate determination of k₁ = (9.8⁺⁹_-5) * 10^-11e^{(-1130+/-190)/T} cm³s^-1 for the F + CF3CFH2 rate constant.A simultaneous fit of the radical decay curves to a mechanism containing the known HO2 self-reaction kinetics, the previously determined CF3CFHO2 self-reaction mechanism, and a cross reaction between these species yields a rate constant of k₇ = (1.8^+2.4_-1.0) * 10^-13e^{(910+/-220)/T} cm³s^-1 for the HO2 + CF3CFHO2 reaction.A product stucy at 296 K by Fourier transform infrared spectroscopy reveals that less than 5percent of the product appears as CF3C(O)F.By inference, >95percent of the reaction gives the hydroperoxide CF3CFHOOH.Implications of these results are discussed with respect to the atmospheric degradation of HFC-134a (CF3CFH2).