Vibrational distribution and dynamics study of the HCN(v 1, v 2, v 3) product in the CN + CH4 hydrogen abstraction reaction

Abstract

A dynamics study of the collisions between the cyano radical and methane is performed at twelve collision energies, between 0.5 and 10.0 kcal mol−1. Using quasi-classical trajectory calculations on an analytical full-dimensional potential energy surface (PES-2017), the results were compared with the previous theoretical study, based on the EVB surface, and with the scarce experimental data. Reaction probability increases with collision energy, reasonably simulating the concave-down shape of the line-of-centres model, but in contrast with the EVB results. Both products, CH3(v) and HCN(v 1, v 2, v 3), present a cold rotational distribution, associated with linear transition-state structures. While the CH3(v) product appears practically in its vibrational ground state, the HCN(v 1, v 2, v 3) product appears vibrationally excited in all modes, especially bending mode, v 2, which reproduces the experimental evidence. Our results show forward–backward product scattering distribution at all collision energies (clearly low collision energies), which differ from the EVB results, where backward scattering is observed at low energies. Finally, when vibrational and rotational restrictions were included in the theoretical analysis, the experimental conditions of future velocity map imaging experiments were simulated, anticipating the dynamics behaviour of the title reaction. Product correlated dynamics properties were reported for comparison with future experiments. In these conditions, the present theoretical results acquire a predictive character and stimulate future experiments.