UV absorption spectra and kinetics of the self reaction of CFCl₂CH₂O₂ and CF₂ClCH₂O₂ radicals in the gas phase at 298 K

Abstract

The ultraviolet absorption spectra of the peroxy radicals derived from hydrochlorofluorocarbons 141b and 142b, (CFClzCHZOz and CFzClCHz02, respectively), and the kinetics of their self reactions have been studied in the gas phase at 298 K using a pulse radiolysis technique. Absorption cross sections were quantified over the wavelength range 220-300 nm. Measured absorption cross sections at 250 nm were indistinguishable within the experimental uncertainties (~10%) and yield;Errors represent the sum of statistical uncertainty and our estimate of potential systematic errors. Our absorption cross section data were then used to derive the observed self reaction rate constants for reactions (1) and (2), defined asCFzCICHzOz + CFzClCHzOz --j products of klobs = (4.36 5 0.64) x lo-'' and k2,,bs = (4.13 -+ 0.58) x lo-'' cm3 molecule-' s-', quoted errors represent 2a. These results are discussed with respect to previous studies of the absorption spectra and kinetics of peroxy radicals

Rate constant for the reaction of F‐atoms with trichloroacetic acid

“… was used by Platz et al to determine k 2 . However, this value should be taken with caution as it does not agree with the earlier results, if pressure dependence is taken into account. As was revealed in the study of Campuzano‐Jost et al, a linear region for all bath gases used (He, Ar, N 2 ) extended to ≈ 20 bar and the high‐pressure plateau was not reached even at maximum pressure of 1000 bar.…”

“… was obtained not by a standard relative‐rate method based on Equation (I), but by varying a k 2 / k 3 parameter to fit a curve of absorbance intensity (total UV absorption by FO 2 and CCl 3 CH 2 O 2 products at 250 nm) versus [CCl 3 CH 3 ]/[O 2 ] ratio, which explains rather low precision of the rate constant ratio. The rate constant of reaction was taken from the absolute measurements under similar conditions carried out using the same technique (UV absorption spectroscopy) . In the bath gas SF 6 and at room temperature, the rate constant was k 3 = (2.4 ± 0.36) (600 mbar), (2.35 ± 0.20) (600 mbar), and (1.93 ± 0.29) (1 bar) in the units of 10 −13 cm 3 molecule −1 s −1 .…”

“…The rate constant of reaction was taken from the absolute measurements under similar conditions carried out using the same technique (UV absorption spectroscopy) . In the bath gas SF 6 and at room temperature, the rate constant was k 3 = (2.4 ± 0.36) (600 mbar), (2.35 ± 0.20) (600 mbar), and (1.93 ± 0.29) (1 bar) in the units of 10 −13 cm 3 molecule −1 s −1 . The most recent value from Ref.…”

Atmospheric Photochemistry of Alternative Halocarbons

“…The only kinetic data for the self-reactions of CFCl,CH,O, and CF,ClCH,O, are the kobs values measured via pulsed radiolysis by Wallington and Nielsen [93]. The presence of a-hydrogen atoms implies the availability of the molecular channel represented by reaction (30); however, the branching ratio is unknown.…”

“…[87,92] and by Wallington and Nielsen [52,93]. The probable reason for the discrepancy stems from the use, by Jemi-Alade et al, of chlorine atoms, as opposed to fluorine atoms, to initiate peroxy radical formation, which were used by the other two groups.…”