Kinetics of formation of chemiluminescent CH(A(2)Delta) by the elementary reactions of C2H(X(2)Sigma(+)) with O(P-3) and O-2(X(3)Sigma(g)(-)): A pulse laser photolysis study

The C2H(X(2) Sigma(+))+O(P-3)-->CH(A(2) Delta)+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 N-2 ensured that both C2H and O were in their X(2) Sigma(+) and P-3 ground states within 1 mu s. The intensity of the resulting CH(A(2) Delta-->X(2) Pi) luminescence was measured, up to 40 mu s 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(P-3)+M-->NO2*+M reaction. The rate constant of the CH(A(2) Delta) forming channel was determined to be (1.8+/-0.7)x10(-11) cm(3) molec(-1) s(-1). The rate constant of the C2H(X(2) Sigma(+))+O-2-->CH(A(2) Delta)+CO2 reaction channel was found to be (3.6+/-1.4)x10(-14) cm(3) molec(-1) s(-1) .