ATMOSPHERIC CHEMISTRY OF HFC-134A - KINETIC AND MECHANISTIC STUDY OF THE CF3CFHO2+HO2 REACTION

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 F-2 in the presence of HFC-134a (CF3CFH2), H-2, and O-2 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 k(1) = (9.8(-5)(+9)) x 10-(11)e(1130+/-190)/T cm(3) S-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 yeilds a rate constant of k(7) = (1.8(-1.0)(+24)) x 10(-13)e((910+/-220)/T) cm(3) s(-1) for the HO2 + CF3CFHO2 reaction. A product study at 296 K by Fourier transform infrared spectroscopy reveals that less than 5% of the product appears as CF3C(O)F. By inference, >95% of the reaction gives the hydroperoxide CF3CFHOOH. Implications of these results are discussed with respect to the atmospheric degradation of HFC-134a (CF3CFH2).