SHOCK-TUBE MEASUREMENTS OF THE REACTIONS OF CN WITH O AND O2

The rate coefficients of the reactions (1) CN + O --> CO + N and (2) CN + O2 --> NCO + O were determined in a series of shock tube experiments from CN time histories recorded using a narrow-linewidth cw laser absorption technique. The ring dye laser source generated 388.44 nm radiation corresponding to the CN B2-SIGMA+(upsilon = 0) <-- X2-SIGMA+(upsilon = 0) P-branch bandhead, enabling 0.1 ppm detection sensitivity. Reaction (1) was measured in shock-heated gas mixtures of typically 200 ppm N2O and 10 ppm C2N2 in argon in the temperature range 3000 to 4500 K and at pressures between 0.45 and 0.90 atm. k1 was determined using pseudo-first order kinetics and was found to be 7.7 X 10(13) (+/- 20%) [cm3 mol-1 s-1]. This value is significantly higher than reported by earlier workers. Reaction (2) was measured in two regimes. In the first, nominal gas mixtures of 500 ppm O2 and 10 ppm C2N2 in argon were shock heated in the temperature range 2700 K to 3800 K and at pressures between 0.62 and 1.05 atm. k2 was determined by fitting the measured CN profiles with a detailed mechanism. In the second regime, gas mixtures of 500 ppm O2 and 1000 ppm C2N2 in argon were shock heated in the temperature range 1550 to 1950 K and at pressures between 1.19 and 1.57 atm. Using pulsed radiation from an ArF excimer laser at 193 nm, a fraction of the C2N2 was photolyzed to produce CN. Pseudo-first order kinetics were used to determine k2. Combining the results from both regimes, k2 was found to be 1.0 X 10(13) (+/- 20%) [cm3 mol-1 s-1].