Direct rate constant measurements for atomic hydrogen + methane .fwdarw. methyl + hydrogen, 897-1729 K, using the flash photolysis-shock tube technique

A kinetic study of the reaction of hydrogen atoms with methane was performed using the Brookhaven flash photolysis-shock tube (FP-ST) facility. Experiments were conducted in the reflected shock regime over the temperature range 897-1,729 K under pseudo-first-order conditions ((CH{sub 4})/(H) {ge} 200). Hydrogen atoms were monitored by using atomic resonance absorption and rate constants were derived directly from decays of absorbance signals. Separate experiments, in which the initial H-atom and radical concentrations were varied, demonstrated the absence of kinetic complications due to secondary reactions. This observation was further verified by the results of a computer modeling study. The rate constant values obtained in this research may be fitted with equal uncertainty to either a two-parameter expression, k{sub 1}(T) = (1.78 {plus minus} 0.12) {times} 10{sup {minus}10} exp({minus}(6,440 {plus minus} 80) K/T), or a three-parameter expression, k{sub 1}(T) = 1.6 {times} 10{sup {minus}19}T{sup 2.57{plus minus}0.76} exp({minus}(3,340 {plus minus} 920) K/T). Units are cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} with uncertainties quoted at the one standard deviation level.