The temperature and pressure dependence of the reaction CH+H2⇔CH3⇔CH2+H

Abstract

Thermal rate constants of the reaction of CH(2Π) with H2 have been measured at pressures between 1 and 160 bar and temperatures between 185 and 800 K. CH radicals have been generated using multiphoton laser flash photolysis of CHBr3 at 248 nm and detected by saturated laser-induced fluorescence near 430 nm. At low pressures the reaction leads to CH2(3B)and H, while at high pressures CH3 radicals are produced. S-shaped transition curves have been constructed to describe the pressure dependence of the rate constant. The high-pressure limiting rate constant for the recombination to CH3 has been evaluated to be k1,∞=2.0×10−10(T/300 K)0,15 cm3molecule−1 s−1. Using experimental low-pressure data from the literature, the rate constant for the second channel could be separated and has been analyzed in terms of SACM theory. A simple kinetic model has been applied to describe the overall rate constant k1 in an extended temperature and pressure range. Related rate constants for the reaction of CH2(3B) with H and the unimolecular two-channel dissociation of CH3 have also been analyzed.