Mechanism of CO fourth positive v u v chemiluminescence in the atomic oxygen reaction with acetylene. Production of C(3P, 1D)

CO(A 1Π−X 1Σ) emission from the O/C2H2 reaction has been studied in a room temperature discharge flow system at pressures from 0.6 to 10 torr. Spectrometric measurements showed that CO(A 1Π) excitation extends to at least ν′ = 12, with anomalously large populations of the ν′ = 1, 4 and 6 levels. The overall emission intensity increases with increasing [Ar], [N2], and [He]. The presence of C(3P and 1D) atoms has been observed via resonance fluorescence. The probable CO(A 1Π)-formation mechanism is O + C2O → CO* + CO, followed by collision-induced cross relaxation: CO* + M → CO(A 1Π) + M, where CO* is identified as a CO state having a potential energy curve which overlaps that of CO(A 1Π), i.e., the d3Δ, e3Σ, a′3Σ and/or D1Δ states. The hypothetical reaction C + O + M → CO(A 1Π) + M does not populate CO(A 1Π) to a significant degree.