Acetylene—Oxygen Reaction in Shock Waves. Origin of CO2

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Abstract
The ir emissions from CO and CO2, formed in the C2H2–O2 reaction in a shock tube, have been observed as a function of time. By calibrating these emissions in terms of concentrations and by comparing them with the emission of CH* (A 2Δ→X 2π), produced in the same reaction, it has been possible to confirm that CO2 is formed in the early stages by a reaction other than CO+OH→CO2+H. This reaction involves a primary carbon-containing radical and an O2 molecule, and its rate at 1800°K is 5% of the rate of formation of CO, produced by a similar reaction. The importance of the reaction CO+OH→CO2+H in the later stages of oxidation has been examined as a function of the initial O2/C2H2 ratio, and the growth of OH concentration during the reaction elucidated. More decisive proof is given that CH* is produced by a reaction which is second order in reaction intermediates.