A shock tube study of methane decomposition using laser absorption by CH3

The pyrolysis of methane was studied in the temperature range 1790 to 2325K, pressure range 0.56 to 3.76 atm, and CH4 mol fraction range 200 ppm to 1.0% in reflected shock wave experiments. The rate coefficient, k1, for methane decomposition, CH4 + Ar → CH3 + H + Ar was determined by comparing measurements of CH3 concentrations made using a narrowlinewidth CW laser absorption technique with CH3 concentrations calculated using a reaction mechanism adapted from Miller and Bowman (1989). Reactant mixture compositions and the experimental conditions were selected so that the early-time CH3 concentration profiles were sensitive almost exclusively to the rate of reaction (1). The least-squares fit to 25 early-time CH3 profiles yielded a bimolecular rate coefficient expression k1 = 8.17 × 1016 exp (−44030/T[K])[cm3/mol/s]. The measured bimolecular rate coefficients were found to be independent of pressure in the range studied. The present determination is similar to the previously-published values summarized by Cobos and Troe (1990) and differs from the recent determination of Klemm et al. (1991).