KINETICS OF THE REACTION C2H-K USING LASER FLASH KINETIC INFRARED-ABSORPTION SPECTROSCOPY(O2 FROM 193 TO 350)

Rate coefficients for the reaction C2H + O2 are measured from 193 to 3 50 K by using transient absorption spectroscopy with an infrared color center laser. Ethynyl radicals are produced by pulsed laser photolysi s of C2H2 in a temperature variable flow cell and a tunable color cent er laser probes the transient removal Of C2H (X2SIGMA+(0,0,0)) in abso rption. The rate coefficient has a slight negative temperature depende nce over the range 193-350 K which can be expressed as k(O2) = (1.5 +/ - 0.3) X 10(-11) exp[(230 +/- 36)/T] cm3 molecule-1 s-1. The lack of a pressure dependence under our experimental conditions strongly sugges ts that the HCCOO complex is short lived with respect to encountering a collision and rapidly dissociates to products without competition f rom collisional stabilization to HCCOO or collisionally induced dissoc iation to reactants.