Kinetics of the Reactions of Allyl and Propargyl Radicals with CH3

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) × 10 16 atom cm -3 . The observed overall C 3 H 5 + CH 3 (1) and C 3 H 3 + CH 3 (2) rate constants demonstrate negative temperature dependencies. Master equation modeling of collisional effects indicates that the C 3 H 5 + CH 3 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: k 1 ∞ = 1.55 × 10 -9 T -0.54 exp(117 K/ T ) cm 3 molecule -1 s -1 . The temperature dependence of k 1 ∞ combined with the thermochemistry of reaction 1 results in the rate constants of the reverse reaction of thermal decomposition of 1-C 4 H 8 k - 1 ∞ (T) = 1.1 × 10 16 exp(−39100 K/ T ) s -1 . On the other hand the C 3 H 3 + CH 3 reaction is not near the high-pressure limit and falloff in reaction 2 cannot be neglected at temperatures above 500 K. Falloff corrections applied to reaction 2, on average, reach a factor of 2 at 800 K and introduce substantial uncertainties in the extrapolated high-pressure-limit rate constant values. The evaluated high-pressure-limit rate constants of reaction 2 can be represented with the expression k 2 ∞ = 6.80 × 10 -11 exp(130K/ T ) cm 3 molecule -1 s -1 . C 4 H 8 and C 4 H 6 were identified as primary products of the reactions 1 and 2, respectively.