The Reaction Rates of Amidogen and Ammonia with Nitrous Oxide: Implications for Combustion Mechanisms

Pulsed laser photolysis experiments with laser-induced fluorescence detection of NH₂ set an upper limit to the rate constant for reaction with N₂O of k < 1 × 10^–15 cm³ molecule^–1 s^–1 at 513 K. Computations were based on geometries and anharmonic frequency analysis (B2PLYP-D3/cc-pVTZ) followed by coupled cluster calculations extrapolated to the infinite basis set limit, with corrections for core–valence electron correlation, scalar relativistic effects, and correlation up to CCSDT(Q). Species that showed multireference character were quantified with MRCI(7,7)+Q/cc-pVTZ theory. Rate constants were obtained for the dominant product channel H₂NN + NO, along with HN₃ + OH, H₂NO + N₂, NNH + HNO, ON(NH)₂ and HNNH + NO. The last channel is slow even at 2500 K, contrary to an early empirical estimate and confirming recent suggestions. Modeling of literature experiments on oxidation of NH₃ by N₂O shows that all channels are too slow to make a significant impact on the loss of N₂O in ammonia flames. Similarly, the direct NH₃ + N₂O reaction is found to be negligibly slow.