STUDY OF THE RECOMBINATION REACTION CH3 + CH3 C2H6. EXPERIMENT

Article abstract of DOI:10.1021/j100320a015

The recombination of methyl radicals has been studied as a function of temperature and bath gas density to obtain more detailed knowledge of the kinetics of this reaction in the unimolecular falloff region.The reaction was studied by two techniques: (1) use of a tubular reactor coupled to a photoionization mass spectrometer; (2) use of absorption spectroscopy with a stainless steel flow cell.In both cases, methyl radicals were generated homogeneoudly by the pulsed photolysis of acetone at 193 nm.CH3 decay profiles were monitored in real-time experiments.Absolute CH3 concentrations were obtained from direct measurements of acetone photodecomposition in the photoionization experiments and from previously determined cross sections in the absorption experiments.Rate constants for the CH3 + CH3 reaction are reported, with argon as the bath gas, at nine temperatures in the 296-906 K and at gas densities from 1.8E16 to 1.4E19 molecules cm^-3.A significantly narrower range of conditions was used in additional experiments using helium as the bath gas.The result obtained are compared with theoretical values of the CH3 + CH3 recombination rate constant obtained in part 2 (following paper in this issue).The combined result of the experimental and theoretical study of this reaction provide a more quantitative description of the role of collisions in this important recombination process.The uncertainty associated with extrapolating unimolecular rate constants to higher temperatures by using a common functional representation of the pressure and temperature dependence of such rate constants is illustrated with a comparison of theory and extrapolation up to 2000 K for the CH3 + CH3 high-pressure-limit rate constant.