A SHOCK-TUBE STUDY OF REACTIONS OF C ATOMS AND CH WITH NO INCLUDING PRODUCT CHANNEL MEASUREMENTS

The reactions of C atoms and CH with NO, which are believed to be initial steps in the NO reburning reaction mechanism, were studied at high temperature behind reflected shock waves. C atoms were formed by pyrolysis or photolysis of dilute mixtures of C3O2 in argon or by pyrolysis of dilute mixtures of CH4 in argon. CH was formed from the pyrolysis of dilute mixtures of CH4 or C2H6 (<30 ppm) in argon. C atoms were detected by use of atomic resonance absorption (ARAS) at 156.1 nm. CH was detected by CW, narrow-line-width laser absorption at 431.131 nm. In the presence of excess NO, C atoms formed by pyrolysis or photolysis rapidly were removed by C(3P) + NO --> products (1). A first-order kinetic analysis led to a rate coefficient k1 = 4.8 X 10(13) (+/- 45%) cm3 mol-1 s-1 over the temperature range 1550-4050 K and pressure range 0.5-1 atm. In order to determine the rate coefficient of CH(X2-PI) + NO --> products (2), a perturbation technique was employed. In this technique, the CH concentration profile resulting from pyrolysis of CH4 or C2H6 diluted in argon was perturbed by the addition of NO. A detailed analysis of the CH profiles led to the rate coefficient k2 = 1.0 X 10(14) (+/- 50%) cm3 mol-1 s-1 over the temperature range 2570-3790 K and pressure range 0.6-1.1 atm. The product channels of reactions 1 and 2 were studied by measuring the formation of product species, CN, N atoms O atoms, OH, and NH, using laser absorption or ARAS. The branching ratios of the product channels of reaction 1, C(3P) + NO --> CN + O (1a) and C(3P) + NO --> CO + N (1b), are k1a/k1 = 40% and k1b/k1 = 60%, independent of temperature from 2430 to 4040 K. The product channels of reaction 2 leading to the formation of NH or OH are less than 10% and 30% of the reaction, respectively. Thus, the principle product channel or reaction 2 is most probably CH(X2-PI) + NO --> HCN + O (2a) over the temperature range 2600-3800 K.