Kinetics of formation of chemiluminescent CH(A 2Δ) by the elementary reactions of C 2H(X 2Σ+) with O( 3P) and O 2(X 3Σg−): A pulse laser photolysis study

Abstract

The C 2 H(X 2 Σ +) + O( 3 P) → CH(A 2Δ) + CO reaction channel has been proposed as a source of the 430 nm CH ∗ chemiluminescence in hydrocarbon flames and in C 2H 2/O/H systems. We present the first measurement of its rate constant. The reactants were generated in known amounts by co-photolysis of C 2H 2 and N 2O at T = 295 K by 193 nm ArF excimer laser pulses. The presence of a large excess of N 2 ensured that both C 2H and O were in their X 2 Σ + and 3P ground states within 1 μs. The intensity of the resulting CH(A 2Δ /ar X 2Π) 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( 3 P) + M → NO 2 ∗ + M reaction. The rate constant of the CH(A 2Δ) forming channel was determined to be (1.8 ± 0.7) × 10 −11cm 3molec −1s −1. The rate constant of the C 2 H(X 2Σ +) + O 2 → CH(A 2Δ) + CO 2 reaction channel was found to be (3.6 ± 1.4) × 10 −14 cm 3 molec −1 s −1 .