TEMPERATURE AND PRESSURE-DEPENDENCE OF THE REACTION CH + H2

The reaction CH(X2II) + H-2 was studied as a function of temperature in the range 200-400 K at 4 Torr total pressure and as a function of total pressure in the range 2-591 Torr at 298 K. CH radicals were generated by excimer laser photolysis of CHClBr2/Ar mixtures and were detected by laser-induced fluorescence. The reaction proceeds along two pathways: Above 300 K, production of CH2 + H dominates with an activation energy of 13.82 +/- 4.19 kJ.mol-1, whereas below 300 K, the rate constants exhibit a negative temperature dependence with an activation energy of -6.12 +/- 1.93 kJ.mol-1 consistent with an adduct formation followed by collisional stabilization. The limiting rate constants k0 and k-infinity and the broadening factor F(c) were determined from the pressure dependence. A transition-state-theory model was applied to analyze the experimental results.