A SHOCK-TUBE STUDY OF THE REACTIONS OF NH WITH NO, O2, AND O

The reactions of NH(X3-SIGMA-) with NO, O2, and O have been studied in reflected and incident shock wave experiments. The source of NH in all the experiments was the thermal dissociation of isocyanic acid, HNCO. Time-histories of the NH(X3-SIGMA) and OH(X2PI) radicals were measured behind the shock waves using cw, narrow-linewidth laser absorption at 336 nm and 307 nm, respectively. The second-order rate coefficients of the reactions: (3) NH + NO-->products (4) NH + O2-->products (5) NH + O-->products were determined to be: k3 = 1.7 x 10(14) exp(-6400/T,K) (f = 0.65, F = 1.5) T = 2220 - 3350 K, k4 = 3.5 x 10(13) exp(-8600/T,K) (f = 0.65, F = 1.5) T = 2200 - 3270 K, and k5 = 9.2 x 10(13) (f = 0.60, F = 1.6) T = 2730 - 3380 K cm3 mol-1 s-1, where f and F define the lower and upper uncertainty limits, respectively. The branching fraction of channel (3(b)), (3(b)) NH + NO-->N2 + OH defined as k3b/k3total, was determined to be 0.19 +/- 0.10 over the temperature range of 2940 K to 3040 K.