The recombination of hydrogen atoms with nitric oxide at high temperatures

Abstract

The rate constant for the H+NO+N₂ reaction (R1,N₂) has been determined in the temperature range 1000–1170K from flow-reactor experiments on the CO/O₂/H₂O/N₂ system perturbed with different amounts of NO. The initiation temperature of this system is highly sensitive to reaction R1, which is the rate-controlling step in the nitric oxide catalyzed removal of hydrogen atoms. Based on the flow-reactor results and the limited amount of data reported in literature, a rate constant for the H+NO+N₂ reaction of 4.0×10²⁰T^−1.75 cm⁶/(mol²s) was determined. This value is in good agreement with the recent result of Allen and Dryer at 1000K but significantly lower at high temperatures than the recommendation of Tsang and Herron. With the recently determined value of ΔH_f,298 (HNO) of 26.0 kcal/mol, which is 2 kcal/mol higher than previous estimates, our results correspond to a rate constant of 1.7×10¹⁹T^−1.5 exp(−23,400/T) cm³/(mol s) for the HNO+N₂ dissociation reaction in the 1000–2500 K range. The sharp drop-off in the rate constant for H+NO+M at high temperatures suggested by the flow-reactor results are supported by reinterpretation of data reported in literature on H₂/O₂/N₂ flames doped with NO. Theoretical considerations suggest that the effect can be attributed to weak-collision effects.