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.