The Rate Coefficient for CH₃ + H₂ → CH₄ + H Measured in Reflected Shock Waves; A Non-Arrhenius Reaction

Dynamic sampling of reacting gas mixtures behind reflected shock waves has been used to determine the concentration vs. time profiles of the products of the recombination chain reactions of methyl radicals in the presence of molecular H 2 . The radicals were produced by the rapid pyrolysis of azomethane. By analysis of profiles from experiments in the temperature range 1272–1370°K we have deduced a value of the rate coefficient of reaction 5: CH 3 + H 2 → CH 4 + H.[Formula: see text]It is shown that although this value of k 5 does not lie on the Arrhenius line drawn through lower temperature data, it does lie close to the upward curved Arrhenius plot of values of k 5 calculated by the B.E.B.O. transition state method. Taking a mean activation energy calculated by the B.E.B.O. method, our results suggest the following description for k 5 over the temperature range 1200 to 2000°K:[Formula: see text]