Determination of the CH + O2 product channels

Abstract

The multichannel CH + O₂ reaction was studied at room temperature, in a low-pressure fast-flow reactor. CH radical was obtained from the reaction of CHBr₃ with potassium atoms. The overall rate constant was determined from the decay of CH with distance, O₂ being introduced in excess. The result, after corrections for axial and radial diffusion, is k = (3.6 ± 0.5) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The OH(A²Σ⁺) chemiluminescence was observed, confirming the existence of the OH + CO channel. The vibrational population distribution of OH(A²Σ⁺) is 32% in the ν′ = 1 level and 68% in the ν′ = 0 level (±5%). The relative atomic concentrations were 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 density (O + HCO). Ab initio calculations of the transition structures have been performed, associated with statistical estimations. The estimated branching ratios are: O + HCO, 20%; O + H + CO, 30%; H + CO₂, 30%; and CO + OH, 20%.