Three-dimensional quantum mechanical study of the NH(X3Σ−)+NO reaction

A three-dimensional quantum mechanical scattering study of the NH(X³Σ⁻)+NO reaction was carried out in the framework of the nonreactive infinite-order sudden approximation (IOSA) using a global HNNO potential energy surface able to describe branching into the H+N₂O and N₂+OH reaction product channels. Negative imaginary potentials (NIPs) were employed to decouple the product channels, avoiding the need to explicitly treat the Schrödinger equation in the product channels and hence eliminating the complicated transformation between the various sets of Jacobi coordinate systems. Absolute integral reactive cross sections were calculated for different translational energies in the range 0.05–0.50 eV and were used to determine the thermal rate coefficient k(T) in the temperature range 300≤T≤5000 K. Comparison with experimental overall rate measurements indicates that the potential energy surface used in the present quantum scattering calculations has a too narrow cone of acceptance leading to a calculated room-temperature rate constant that is about a factor of 10 lower than the experimental ones. Good agreement between theoretical and recent experimental rate constants was obtained in the temperature range T=1200–2000 K. Comparison of the theoretical results with experimental data obtained at T>2000 K indicates that the inclusion of the NNH+O reaction product channel into the global HNNO potential energy surface is necessary in order to accurately describe the measured temperature dependence of the overall NH(X³Σ⁻)+NO rate constant in the high-temperature region 2000<T<5000 K.