The NO‐ and NO 2 ‐catalyzed decomposition of I 2 in shock waves

Measurements of the NO‐catalyzed dissociation of I 2 in Ar in incident shock waves were carried out in the temperature range of 700°‐1520°K and at total concentrations of 5 × 10 −6 ‐6 × 10 −5 mol/cm 3 , using ultraviolet‐visible absorption techniques to monitor the disappearance of I 2 . It was shown that the main reaction responsible for the disappearance under these conditions is I 2 + NO → INO + I, for which a rate coefficient of (2.9 ± 0.5) × 10 13 exp[‐(18.0 ± 0.6 kcal/mol)/ RT ] cm 2 /mol·sec was determined. The INO formed dissociates rapidly in a subsequent reaction. The reaction, therefore, constitutes a “chemical model” for a “thermal collisional release mechanism.” Preliminary measurements of the rate coefficient for I 2 + NO 2 → INO 2 + I are also presented. Combined with information on the reverse reactions obtained in earlier room temperature experiments, these results lead to accurate values of Δ H ° f for INO and INO 2 equal to 29.7 ± 0.5 and 15.9 ± 1 kcal/mol, respectively.