TEMPERATURE-DEPENDENCE OF REACTIONS OF HO2 WITH NO AND NO2

Mixtures of N2O, H2, O2, and trace amounts of NO and NO2 were photolyzed at 213.9 nm, at 245°–328°K, and at about 1 atm total pressure (mostly H2). HO2 radicals are produced from the photolysis and they react as follows: (Formula Presented.) Reaction (1b) is unimportant under all of our reaction conditions. Reaction (1a) was studied in competition with reaction (3) from which it was found that k1a/k31/2 = 6.4 × 10−6 exp { z−(1400 ± 500)/RT} cm3/2/sec1/2. If k3 is taken to be 3.3 × 10−12 cm3/sec independent of temperature, k1a = 1.2 × 10−11 exp {−(1400 ± 500)/RT} cm3/sec. Reaction (2a) is negligible compared to reaction (2b) under all of our reaction conditions. The ratio k2b/k1 = 0.61 ± 0.15 at 245°K. Using the Arrhenius expression for k1a given above leads to k2b = 4.2 × 10−13 cm3/sec, which is assumed to be independent of temperature. The intermediate HO2NO2 is unstable and induces the dark oxidation of NO through reaction (−2b), which was found to have a rate coefficient k−2b = 6 × 1017 exp {−26,000/RT} sec−1 based on the value of k1a given above. The intermediate can also decompose via (Formula Presented.) Reaction (10b) is at least partially heterogeneous. Copyright © 1978 John Wiley & Sons, Inc.