CH(A2Δ) formation in hydrocarbon combustion:: The temperature dependence of the rate constant of the reaction C2H+O2 → CH(A2Δ)+CO2

The temperature dependence of the rate constant of the chemiluminescence reaction C2H + O-2 -> CH(A) + CO2, k(1e), has been experimentally determined over the temperature range 316-837 K using pulsed laser photolysis techniques. The rate constant was found to have a pronounced positive temperature dependence given by k(1e)(T) = AT(4.4) exp(1150 +/- 150/T), where A = 1 x 10(-27) cm(3) s(-1). The preexponential factor for k(1e), A, which is known only to within an order of magnitude, is based on a revised expression for the rate constant for the C2H + O(P-3) -> CH(A) + CO reaction, k(2b), of (1.0 +/- 0.5) x 10(-11) exp(-230 K/T) cm(3) s(-1) [Devriendt, K.; Van Look, H.; Ceursters, B.; Peeters, J. Chem. Phys. Lett. 1996, 261, 450] and a k(2b)/k(1e) determination of this work of 1200 500 at 295 K. Using the temperature dependence of the rate constant k(1e)(T)/k(1e)(300 K), which is much more accurately and precisely determined than is A, we predict an increase in k(1e) of a factor 60 16 between 300 and 1500 K. The ratio of rate constants k(2b)/k(1e) is predicted to change from 1200 500 at 295 K to 40 25 at 1500 K. These results suggest that the reaction C2H + O-2 -> CH(A) + CO2 contributes significantly to CH(A-X) chemiluminescence in hot flames and especially under fuel-lean conditions where it probably dominates the reaction C2H + O(P-3) - CH(A) + CO.