Abstract

The N + N2 exchange rate is calculated using a time-dependent quantum dynamics method on a newly determined ab initio potential energy surface (PES) for the ground 4A" state. This ab initio PES shows a double barrier feature in the interaction region with the barrier height at 47.2 kcal/mol, and a shallow well between these two barriers, with the minimum at 43.7 kcal/mol. A quantum dynamics wave packet calculation has been carried out using the fitted PES to compute the cumulative reaction probability for the exchange reaction of N + N2(J=0). The J -K shift method is then employed to obtain the rate constant for this reaction. The calculated rate constant is compared with experimental data and a recent quasi-classical calculation using a LEPS PES.Significant differences are found between the present and quasiclassical results. The present rate calculation is the first accurate 3D quantal dynamics study for N + N2 reaction system and the ab initio PES reported here is the first such surface for N3.

No abstract

N+2 and O+2 potential energy curves have been constructed by combining measured data with the results from electronic structure calculations. These potential curves have been employed to determine accurate charge exchange cross sections, transport cross sections, and collision integrals for ground state N+ –N and O+ –O interactions. The cross sections have been calculated from a semiclassical approximation to the scattering using our computer code that fits a spline curve through the discrete potential data and incorporates the proper long-range behavior of the interaction forces. The charge exchange cross sections are slightly smaller than the values we reported previously using an asymptotic approximation and also agree well with the results of beam measurements at high energies. The collision integrals are tabulated for a broad range of temperatures 250–100 000 K and are intended to reduce the uncertainty in the values of the transport properties of nonequilibrium air, particularly at high temperatures.

Ab initio calculations employing large basis sets are performed to determine an accurate potential energy surface for H–H2 interactions for a broad range of separation distances. At large distances, the spherically averaged potential determined from the calculated energies agrees well with the corresponding results determined from dispersion coefficients; the van der Waals well depth is predicted to be 75±3μEh. Large basis sets have also been applied to reexamine the accuracy of theoretical repulsive potential energy surfaces (25–70 kcal/mol above the H–H2 asymptote) at small interatomic separations; the Boothroyd, Keogh, Martin, and Peterson (BKMP) potential energy surface is found to agree with results of the present calculations to within the expected uncertainty (±1 kcal/mol) of the fit. Multipolar expansions of the computed H–H2 potential energy surface are reported for four internuclear separation distances (1.2, 1.401, 1.449, and 1.7a0) of the hydrogen molecule. The differential elastic scattering cross section calculated from the present results is compared with the measurements from a crossed beam experiment.