KINETICS OF THE CROSS-REACTIONS OF CH3O2 AND C2H5O2 RADICALS WITH SELECTED PEROXY-RADICALS

The kinetics of The reactions of selected peroxy radicals (RO(2)) with CH3O2 and with C2H5O2 have been investigated using two techniques: ex cimer-laser photolysis and conventional flash photolysis, both coupled with UV absorption spectrometry. Radicals were generated either by ph otolysis of molecular chlorine in the presence of suitable hydrocarbon s or by photolysis of the appropriate alkyl chloride. All such cross-r eaction kinetics were investigated al 760 Torr total pressure and room temperature except for the reaction of the allylperoxy radical with C H3O2, for which the rate constant was determined between 291 and 423 K , resulting in the following rate expression: k(15) = (2.8 +/- 0.7) x 10(-13) exp[(515 +/- 75)/T] cm(3) molecule(-1) s(-1). Values of (2.0 /- 0.5) x 10(-13), (1.5 +/- 0.5) x 10(-12), (9.0 +/- 0.15) x 10(-14), <2.0 x 10(-12), (2.5 +/- 0.5) x 10(-12), and (8.2 +/- 0.6) x 10(-12) ( units of cm(3) molecule(-1) s(-1)) have been obtained for the reaction s of CH3O2 radicals with C2H5O2, neo-C5H11O2, c-C6H11O2, C6H5CH2O2, CH 2ClO2, and CH3C(O)O-2, respectively, and (1.0 +/- 0.3) x 10(-12), (5.6 +/- 0.8) x 10(-13), (4.0 +/- 0.2) x 10(-14), and (1.0 +/- 0.3) x 10(- 11) (units of cm(3) molecule(-1) s(-1)) for the reactions of C2H5O2 wi th CH2=CHCH2O2, neo-C5H11O2, c-C6H11O2, and CH3C(O)O-2 radicals, respe ctively. These rate constants were obtained by numerical simulations o f the complete reaction mechanisms, which were deduced from the known mechanisms of the corresponding peroxy radical self-reactions. A syste matic analysis of propagation of errors was carried out for each react ion to quantify the sensitivity of the cross-reaction rate constant to the parameters used in kinetic simulations. The rate constant for a g iven cross reaction is generally found to be between the rate constant s for the self-reactions of RO(2) and CH3O2 for C2H5O2). However, when the RO(2) self-reaction is fast, the cross reaction with CH3O2, (or C 2H5O2) is also fast, with similar rate constants for both reactions, s uggesting that these particular peroxy radical cross reactions can pla y a significant role in the chemistry of hydrocarbon oxidation process es in the troposphere and in low-temperature combustion. Relationships between cross-reaction and self-reaction rate constants are suggested .