Determination of the CH+O-2 product channels

The multichannel CH + O-2 reaction was studied at room temperature, in a lo w-pressure fast-flow reactor. CH radical was obtained from the reaction of CHBr3 with potassium atoms. The overall rate constant was determined from t he decay of CH with distance, O-2 being introduced in excess. The result, a fter corrections for axial and radial diffusion, is k = (3.6 +/- 0.5) x 10( -11) cm(3) molecule(-1) s(-1). The OH(A (2)Sigma (+)) chemiluminescence was observed, confirming the existence of the OH + CO channel. The vibrational population distribution of OH(A (2)Sigma (+)) is 32% in the nu' = 1 level and 68% in the nu' = 0 level (+/-5%). The relative atomic concentrations we re determined by resonance fluorescence in the vacuum ultraviolet. A ratio of 1.4 +/- 0.2 was found between the H atom density (H atoms being produced from the H + CO2 channel and from the HCO dissociation) and the O atom den sity (O + HCO). Ab initio calculations of the transition structures have be en performed, associated with statistical estimations. The estimated branch ing ratios are : O + HCO, 20%; O + H + CO, 30%; H + CO2, 30%; and CO + OH, 20%.