HIGH-TEMPERATURE REACTION-RATE COEFFICIENTS DERIVED FROM N-ATOM ARAS MEASUREMENTS AND EXCIMER PHOTOLYSIS OF NO

Mixtures of NO and NO/H2 in Ar were shock‐heated and photolyzed with an ArF excimer laser. Measurements in these experiments of N‐atom profiles using atomic resonance absorption spectrophotometry (ARAS) permitted the determination of two rate coefficients. The rate coefficient for the reaction (Formula Presented.) was found to be 4.29 × 1013 exp(−787/T) cm3 mol−1 sec−1 (±20% at 1400 K to ±10% at 3500 K). This is the first direct high temperature measurement of this rate coefficient in the exothermic direction. The rate coefficient for the reaction (Formula Presented.) was found to be 1.60 × 1014 exp(−12650/T) (±35% from 1950 to 2850 K). To our knowledge, this is the first direct measurement of this rate coefficient. A study of the N‐atom ARAS absorption behavior revealed a noticeable pressure dependence, as well as a weak temperature dependence, in the Beer‐Lambert law absorption coefficient. Proper consideration of these effects is important when the N‐atom ARAS diagnostic is used for absolute concentration measurements. Copyright © 1990 John Wiley & Sons, Inc.