Direct measurements of the rate coefficient for the reaction OH+CH 4 → CH 3+H 2O over 300-1500 K

Abstract

The flash photolysis/resonance fluorescence technique for styding OH radical kinetics was extended to temperatures above 1500 K using the High Temperature Photochemistry reactor. In this application to combustion related processes, direct measurements of the rate coefficient for the benchmark reaction, OH+CH4 → CH3+H2O were obtained over the widest temperature range to date on this reaction and are described by the expression: k(T)=10−16.59±0.68 T1.83±0.17 exp [−1396±134/T] cm3 molecule−1 s−1 (298-1512K) This expression ties together previous low and high temperature data, and allows use of the rate coefficient over the measurement temperatures to an estimated accuracy of 10% or better. It also provides a firmer basis for the extrapolation of k(T) to higher temperatures, and allows critical comparison with theoretical calculations. The experimental methods employed are applicable, with minor modifications, to the study of many OH reactions over the temperature range 300-1500 K. An upper limit of ≈ 1600 K was found on the use of H2O as a photolytic source of OH radicals for kinetic studies, due to the thermal dissociation of H2O at higher temperatures.