Reaction of Chlorine Atoms with Methylperoxy and Ethylperoxy Radicals

Abstract

Flash photolysis combined with time-resolved UV spectroscopy and transient I R absorption measurements shows that chlorine atoms react rapidly with CH3O2 and C2H502, producing C10 and C O among other products.The room temperature rate constants are kz = (1.5 f 0.2) X 1O-Io cm3 s-' for both reactions. The distribution of products is interpreted to indicate that the reaction with methylperoxy radicals proceeds via two channels to yield C H 3 0 + C10 with a branching ratio of 0.51 f 0.05 and CH2Oz + HCl with a branching ratio of 0.49 f 0.05. The Criegee intermediate, CH202, has a lifetime of 15 f 5 ps and subsequently decomposes via three channels, with 61 f 7% producing C O + H2O. The ethylperoxy reaction proceeds analogously with a branching fraction of 0.49 f 0.05 for the CzH50 + ClOchannel, but with a C O yield --'/aof the yield from themethylperoxy reaction.

Kinetic studies of Cl-atom reactions with selected aromatic compounds using the photochemical reactor-FTIR spectroscopy technique

“…For Cl-atom reactions with CF 3 O 2 and CF 3 CHFO 2 , no literature data are available. The rate constants in Table III for these two reactions were estimated based on the Cl ϩ CH 3 O 2 reaction, which has been studied in detailed by Maricq et al [38]. The uncertainties in these estimates are not expected to impact the present analysis significantly, because the Cl-atom reactions with CF 3 O 2 and CF 3 CHFO 2 are both relatively minor under the conditions of this experiment due to the low Cl-atom concentration.…”

Atmospheric Photochemistry of Alternative Halocarbons

“…a process that can be very rapid [97]. In the absence of further kinetic information, it is impossible to derive the actual peroxy radical self-reaction rate constant from kobs.…”

Combined experimental and theoretical investisgation of the reactivity of CH3O2 and C2H5O2 radicals

“…(corresponding to R 44a and R 44b in equal amounts 81,116 while Daële and Poulet 82 suggest R 44a as the major channel. Biggs et al 118 have investigated experimentally the reaction of the most simple fluorinated peroxy radical CF3O2 with OH.…”

“…The UV spectra of different peroxy radicals are depicted in Figure 1.3. Due to the significance of CH3O2 radicals in the atmospheric degradation of methane, there has been a wealth of spectroscopic studies of the UV absorption spectrum of this radical from the last fifty years 7,[25][26][27][28][29][30][31][32][33] . Generally, two techniques have been employed: modulated and flash photolysis, both combined with UV absorption spectroscopy.…”

“…The only estimation of the rate constant of the reaction CH3O2 + OH has been carried out by Tsang and Hampson 80 : based on analogy with the reaction of HO2 with OH radicals they recommended for the reaction between CH3O2 and OH a rate constant of k44 = 1.0 × 10 -10 cm 3 s -1 with an estimated uncertainty of a factor of 5. In the absence of any experimental study of R 44, the reaction of CH3O2 radicals with Cl-atoms can serve as proxy: it has been investigated several times 81,82,116,117 and its rate constant is very fast (≈ 1.7 × 10 -10 cm 3 s -1 ), proposed reaction products are either CH3O and CH2O2…”