Re-Examination of the N₂O + O Reaction

The reaction of N₂O with O is a key step in consumption of nitrous oxide in thermal processes. It has two product channels, NO + NO (R₂) and N2 + O2 (R₃). The rate constant for R2 has been measured both in the forward and the reverse direction at elevated temperature and is well established. However, the rate constant for the N₂ + O₂ channel (R₃) has been difficult to quantify and has significant error limits. The direct reaction on the triplet surface has a barrier of around 40 kcal mol^–1, and it is too slow for the N₂ + O₂ channel to have any practical significance. Recently, Pham and Lin (2022) suggested an alternative low activation energy reaction path that involves intersystem crossing and reaction on the singlet surface. In the present work, we re-examined a wide range of experiments relevant for the N₂O + O reaction through kinetic modeling, paying attention to the impact of artifacts such as impurities and surface reactions. Experimental results from shock tubes and batch reactors on the final NO yield in N₂O decomposition, covering temperatures of 973–2200 K and pressures of 0.013–11.5 atm, support k₃ ∼ 0, consistent with the high activation energy for reaction on the triplet surface and a low probability of ISC.