Quasiclassical trajectory treatment of the O++N2→NO++N reaction

Abstract

Quasiclassical trajectory calculations have been carried out as part of an overall effort to understand and predict the O+/N2 reactions. In the present work, a surrogate hypersurface for the low energy adiabatic pathway governing the reaction of ground state reactants is developed. It was found that the presence of a barrier, per se, in the reaction coordinate, produces a qualitatively correct treatment of the experimentally known features. These calculations not only properly reproduce the threshold and peaking behavior of the total cross sections, and the rate enhancement effects of reagent vibrational excitation, they also predict the behavior of the differential and doubly-differential cross sections. From these comparisons, it is presently established that the key features of the N2O+(1 4A″) potential energy surface, in terms of the calculated dynamics properties, is an effective barrier to O+(4S)+N2(X 1Σg+, v⩾0) ranging from 0.2 to 0.5 eV. The use of such a barrier, 0.25 eV, is found to yield nearly quantitative agreement with experiment. This effective barrier results from a combination of potential and dynamics effects and is shown to be composed of a barrier in the potential energy surface of about 0.2–0.3 eV and a ’’steric’’ factor which varies from approximately 0.0–0.2 eV. The vibrational enhancement effect, while significant, is found to be much less important than the translational enhancement effect. That is, near threshold, a given increment of energy added to the reagents increases the reactivity four times as much if it is placed in the translational mode than if it is placed in the vibrational mode.