A global potential energy surface, entrance channel recrossing and the applicability of capture theory

A global potential energy surface for the CN 2 system has been developed with the aim of studying the N + CN → C + N 2 reaction at low temperatures. A three-dimensional analytic functional form has been fit to CASPT3/cc-pVQZ energies. Classical trajectory simulations on this fitted representation of the potential show a significant proportion of trajectories returning to the entrance channel after forming the CN 2 intermediate, violating a key assumption of capture theory. While the fitted potential is considered inappropriate for calculating accurate low-temperature thermal rate constants, the potential can be used in future studies of the poorly characterised N + CN and C + N 2 reactions at temperatures relevant to combustion.