BRANCHING RATIO OF THE REACTION NH2+NO AT ELEVATED-TEMPERATURES

The branching ratios into the OH and H2O producing channels in the reaction of NH2 with NO have been measured at four temperatures ranging from.room temperature to 900-degrees-C. The reaction was initiated by production of NH2 by excimer laser photolysis of ammonia at 193 nm in the presence of nitric oxide and was probed using a color center laser in conjunction with fast IR detectors. Upon photolysis, the NH3 infrared absorption decreases with consequent appearance of NH2 infrared absorption lines. The magnitude of the decrease in the NH3 infrared absorption is compared with infrared absorbance of OH and H2O produced by the reaction. Measurement of room temperature peak absorption cross sections for NH3, NH2, and H2O combined with the literature value of the OH cross section permits the determination of the branching ratios. For elevated temperatures, the appropriate Boltzmann factors and partition functions were used to calculate the required cross sections from the room temperature values. The branching ratio into the OH channel was observed to increase from 10% at room temperature to 17% at 900-degrees-C. However, the total contribution of the two channels decreased from almost-equal-to 94% at 26-degrees-C to almost-equal-to 70% at 900-degrees-C, possibly indicating the onset of an additional reaction channel. The possibility that the OH signal might arise from an artifact source was investigated.