Kinetics of the Reactions of Allyl and Propargyl Radicals with CH3

Abstract

The allyl-methyl and propargyl-methyl cross-radical reactions were studied by laser photolysis/photoionization mass spectroscopy. Overall rate constants were obtained in direct real-time experiments in the temperature region 301−800 K and bath gas (helium) density (3−36) × 1016 atom cm-3. The observed overall C3H5 + CH3 (1) and C3H3 + CH3 (2) rate constants demonstrate negative temperature dependencies. Master equation modeling of collisional effects indicates that the C3H5 + CH3 reaction is near its high-pressure limit under all experimental conditions used. Minor corrections for the falloff effects (on average, 18% at the highest temperature) applied to the experimental values result in the high-pressure-limit temperature dependence of the rate constant of reaction 1: k1∞ = 1.55 × 10-9 T -0.54exp(117 K/T) cm3 molecule-1 s-1. The temperature dependence of k1∞ combined with the thermochemistry of reaction 1 results in the rate constants of the reverse reaction of thermal decomposition of 1-C4H8 k-1∞(T) =...