Dynamics study of the OH + NH hydrogen abstraction reaction using QCT calculations based on an analytical potential energy surface

To understand the reactivity and mechanism of the OH + NH → HO + NH gas-phase reaction, which evolves through wells in the entrance and exit channels, a detailed dynamics study was carried out using quasi-classical trajectory calculations. The calculations were performed on an analytical potential energy surface (PES) recently developed by our group, PES-2012 Monge-Palacios J. Chem. Phys. 138, 084305 (2013)10.1063/1.4792719. Most of the available energy appeared as HO product vibrational energy (54%), reproducing the only experimental evidence, while only the 21% of this energy appeared as NH co-product vibrational energy. Both products appeared with cold and broad rotational distributions. The excitation function (constant collision energy in the range 1.0-14.0 kcal mol) increases smoothly with energy, contrasting with the only theoretical information (reduced-dimensional quantum scattering calculations based on a simplified PES), which presented a peak at low collision energies, related to quantized states. Analysis of the individual reactive trajectories showed that different mechanisms operate depending on the collision energy. Thus, while at high energies (E ≥ 6 kcal mol ) all trajectories are direct, at low energies about 20%-30% of trajectories are indirect, i.e., with the mediation of a trapping complex, mainly in the product well. Finally, the effect of the zero-point energy constraint on the dynamics properties was analyzed. © 2013 AIP Publishing LLC.