A SHOCK-TUBE STUDY OF REACTIONS OF ATOMIC OXYGEN WITH ISOCYANIC ACID

Reactions of atomic oxygen with isocyanic acid (HNCO) have been studied in incident and reflected shock wave experiments using HNCO/N2O/Ar mixtures. Quantitative time-histories of the NH(X(3)SIGMA-) and OH(X(2)PI(i)) 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: (2a) O + HNCO --> NH + CO2 and (2c) O + HNCO --> OH + NCO were determined from early-time NH and OH formation rates, with least-squares two-parameter fits of the results given by: k2a = 1.9 x 10(13) exp(-7150/T,K) (f = 0.62, F = 1.52) T = 2120-2500 K and k2c = 1.4 x 10(14) exp(-10300/T,K) (f = 0.65, F = 1.35) T = 2120-3190 K, cm3 mol-1 s-1. The minimum and maximum rate constant factors (f,F) define the lower and upper uncertainty limits, respectively. An upper limit on the rate coefficient of (3) OH + HNCO --> products was determined to be: k3 less-than-or-equal-to 1.5 x 10(12) cm3 mol-1 s-1, T = 2120-2350 K.