Kinetics of formation of chemiluminescent CH(A2Δ) by the elementary reactions of C2H(X2 Σ+) with O(3P) and O2(X3Σg−): A pulse laser photolysis study

The C2H(X2 Σ+) + O(3P) → CH(A2Δ) + CO reaction channel has been proposed as a source of the 430 nm CH∗ chemiluminescence in hydrocarbon flames and in C2H2/O/H systems. We present the first measurement of its rate constant. The reactants were generated in known amounts by co-photolysis of C2H2 and N2O at T = 295 K by 193 nm ArF excimer laser pulses. The presence of a large excess of N2 ensured that both C2H and O were in their X2Σ+ and 3P ground states within 1 μs. The intensity of the resulting CH(A2Δ /ar X2Π) luminescence was measured, up to 40 μs after the excimer pulse, using a 429.5 ± 4.0 nm interference filter and a photomultiplier. Calibration was achieved via the known spectral photon yield of the NO + O(3P) + M → NO2∗ + M reaction. The rate constant of the CH(A2Δ) forming channel was determined to be (1.8 ± 0.7) × 10−11cm3molec−1s−1. The rate constant of the C2H(X2Σ+) + O2 → CH(A2Δ) + CO2 reaction channel was found to be (3.6 ± 1.4) × 10 −14cm3molec−1s−1.