UV ABSORPTION-SPECTRUM, AND KINETICS AND MECHANISM OF THE SELF-REACTION OF CF3CF2O2 RADICALS IN THE GAS-PHASE AT 295-K

The ultraviolet absorption spectrum, kinetics, and mechanism of the se lf reaction of CF3CF2O2 radicals have been studied in the gas phase at 295 K. Two techniques were used; pulse radiolysis UV absorption to me asure the spectrum and kinetics, and long-path length FTIR spectroscop y to identify and quantify the reaction products. Absorption cross sec tions were quantified over the wavelength range 220-270 nm. At 230 nm, sigma(CF3CF2O2) = (2.74 +/- 0.46) x 10(-18) cm2 molecule-1. This abso rption cross section was used to derive the observed self reaction rat e constant for reaction (1), defined as, -d[CF3CF2O2]/dt = 2k(lobs)[CF 3CF2O2]2: (1) CF3CF2O2 + CF3CF2O2 --> products k(lobs) = (2.10 +/- 0.3 8) x 10(-12) cm3 Molecule-1 s-1 (2sigma). The observed products follow ing the self reaction of CF3CF2O2 radicals were COF2, CF3O3CF3, CF3O3C 2F5, and CF3OH. CF3O2CF3 was tentatively identified as a product. The carbon balance was 90-100%. The self reaction of CF3CF2O2 radicals was found to proceed via one channel to produce CF3CF2O radicals which th en decompose to give CF3 radicals and COF2. In the presence of O2, CF3 radicals are converted into CF3O radicals. CF3O radicals have several fates; self reaction to give CF3O2CF3; reaction with CF3O2 radicals t o give CF3O3CF3; reaction with C2F5O2 radicals to give CF3O3C2F5; or r eaction with CF3CF2H to give CF3OH. As part of this work a rate consta nt of (2.5 +/- 0.6) X 10(-16) cm3 molecule- s - 1 was measured for the reaction of Cl atoms with CF3CHF2 using a relative rate technique. Re sults are discussed with respect to the atmospheric chemistry of CF3CF 2H (HFC-125). (C) 1993 John Wiley & Sons, Inc.