Abstract: | 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 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 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. |