Direct Measurement of the Rate Constant for CH3 + OH Recombination at 290 K

Abstract

AbstractPreliminary rate data for reaction magnified image under pseudo‐first‐order conditions of excess CH3, are reported at 290 K, covering a 7 – 700 Torr pressure range. The radicals were generated by laser flash photolysis of CH3COCH3 and HNO3 at 193 nm and detected by absorption (216.36 nm, CH3) and laser induced fluorescence (excitation at 282 nm and detection at 308 nm, OH). The rate constants were determined by fitting to a 3 parameter analytical expression and to a 15 reaction model by numerical integration. The two techniques gave results in good agreement. The pressure dependence of the rate constant was fitted using inverse Laplace transformation to obtain microcanonical rate constants which were incorporated in a chemical activation master equation model. The limiting high pressure rate constant obtained at 290 K is (7.6 ± 0.8) · 10−11 cm3 molecule−1 s−1, where the error limits represent ±2σ. Combining the experimental data with those of Oser et al. at lower pressures suggests that there is an incompatibility between these results, those of W. Hack et al. and the enthalpy of formation of 1CH2.