RATE CONSTANTS FOR THE REACTIONS O+C2H2 AND O+C2D2 -] PRODUCTS, OVER THE TEMPERATURE-RANGE APPROXIMATELY 850-1950-K, BY THE FLASH-PHOTOLYSIS SHOCK-TUBE TECHNIQUE - DETERMINATION OF THE BRANCHING RATIO AND A FURTHER THEORETICAL-ANALYSIS

Overall rate constants for the reactions O + C2H2 → products and O + C2D2 → products have been measured between ∼850 and 1950 K by the flash photolysis-shock tube (FP-ST) technique. The results can be well represented by the Arrhenius equations k1H = (1.78 ± 0.18) × 10-10 exp(-2714 ± 118 K/T), and k1D = (1.73 ± 0.24) × 10-10 exp(-2740 ± 167 K/T), where both are expressed in units of cm3 molecule-1 s-1. The branching ratio for the process O + C2H2 → HCCO + H has been estimated by comparison experiments to the reaction O + H2 → OH + H, under identical conditions of first-order O-atom depletion, photolyte concentration, and flash energy. The result is that the H-atom-producing channel amounts to 0.80 ± 0.15 of the overall reaction between 900 and 1200 K. The present results on O + C2H2 are compared to earlier lower and higher temperature studies. A three-parameter evaluation of the overall rate behavior is derived from the present and all earlier studies, and the result, between 195 and 2500 K is k1 = 1.2 × 10-17 T2.09 exp(-786 K/T) cm3 molecule-1 s-1. The theoretical studies on the title reactions by Harding and Wagner are reviewed and extended in order to understand the theoretical implications concerning the overall rate behavior. © 1990 American Chemical Society.