Kinetics of the self-reactions of peroxy radicals arising from chlorine-initiated oxidation of chloroethenes

The kinetics of the self-reactions of CHCl2CHClO2, CHCl2CCl2O2, and CCl3CCl 2O2 have been investigated using a conventional flash photolysis/UV absorpt ion setup at room temperature and at atmospheric pressure. The UV absorptio n spectra of CHCl2CHClO2, CHCl2CCl2O2, and CCl3CCl2O2 were determined betwe en 230 and 290 nm. All spectra present a broad band centered around 250 nm, with a decrease of cross sections going from the less chlorinated to the m ore chlorinated radicals. Spectra of CCl3C(O)Cl and CHCl2C(O)Cl. formed in the self-reactions of CCl3CCl2O2 and CHCl2CHClO2 respectively, were also me asured between 220 and 290 nm. Values of (3.6 +/- 0.9) x 10(-12), (7.0 +/- 1.5) x 10(-12), and (5.0 +/- 1.5) x 10(-12) (units of cm(3) molecule(-1) s( -1), statistical errors 2 sigma) have been obtained at 298 K for the rate c onstants of the self-reactions of CHCl2CHClO2, CHCl2CCl2O2, and CCl3CClO2 r adicals, respectively. Kinetic analyses of self-reactions were very sensiti ve to the reaction mechanism used and, in particular, to the way chloroetho xy radicals reacted. Our experimental observations are totally consistent w ith end-product studies reported in the literature and provide a valuable c onfirmation of the mechanisms. As the determination of rate constants depen ds on complex reaction systems, a total uncertainty factor of nearly 2 has been estimated for all rate constants measured, and no clear reactivity tre nd can be extracted from these data. Nevertheless, we propose for the rate constants of chloroethylperoxy radical self-reactions an average value of ( 5 +/- 2) x 10-'2 cm3 molecule(-1) s(-1) at 298 K.