Kinetic Study on Reactions of 1- and 2-Methylvinoxy Radicals with O₂

The reactions of 1- and 2-methylvinoxy radicals with O₂ have been studied by laser-induced fluorescence coupled with pulsed laser photolysis of precursor molecules at room temperature (298 ± 5 K). The rate constants for both reactions showed typical falloff pressure dependence in the investigated pressure range (8−330 Torr, He buffer), which suggests the dominance of recombination processes to form peroxy radicals. From the Rice−Ramsperger−Kassel−Morcus fit to the experimental data, the limiting high-pressure rate constants were derived to be k^∞ (1-methylvinoxy + O₂) = 9.8 × 10^-13 and k^∞ (2-methylvinoxy + O₂) = 1.3 × 10^-12 cm³ molecule^-1 s^-1, which are 5−7 times larger than that for the reaction of a nonsubstituted vinoxy radical. The influence of the methyl substituent effect and the resonance stabilization on the rate constants is discussed.