ULTRAVIOLET-ABSORPTION SPECTRUM AND KINETICS AND MECHANISM OF THE SELF-REACTION OF CHF2CF2O2 RADICALS IN THE GAS-PHASE AT 298-K

The ultraviolet absorption spectrum and kinetics and mechanism of the self-reaction of CHF2CF2O2 radicals have been studied in the gas phase at 298 K. Two techniques were used: pulse radiolysis UV absorption to measure the spectrum and kinetics and long-path-length Fourier transform infrared spectroscopy (FTIR) to identify and quantify the reaction products. Absorption cross sections were quantified over the wavelength range 220-270 nm. At 230 nm, sigma(CHF2CF2O2) = (3.2 +/- 0.5) X 10(-18) cm2 molecule-1. Errors are statistical (2 standard deviations) plus our estimate of potential systematic uncertainty (15%). This absorption cross section was used to derive the observed self-reaction rate constant for the reaction CHF2CF2O2 + CHF2CF2O2 --> products (1), defined as -d[CHF2CF2O2]/dt = 2k(lobs)[CHF2CF2O2]2. k(l,obs) = (2.7 +/- 0.6) x 10(-12) cm3 molecule-1 s-1 (errors are 2 standard deviations). Measured UV transients were not corrected for possible complications caused by formation of CHF2O2 and HO2 radicals. Hence, k(l,obs) may not be the true bimolecular rate constant for reaction 1. The only carbon-containing product observed by FTIR spectroscopy was COF2. The carbon balance was, within our experimental uncertainty, 100%. As part of this work, a rate constant of (1.9 +/- 0.2) x 10(-15) cm3 molecule-1 s-1 was measured for the reaction of Cl atoms with CHF2CHF2 using a relative rate technique. Results are discussed with respect to the atmospheric chemistry of haloalkanes.