High-resolution total differential cross sections for scattering of helium by O2, N2, and NO

Abstract

High-resolution crossed molecular beam measurements of the total differential cross sections (DCS) for the scattering of He by O2, N2, and NO in the thermal energy range are reported. The data show well resolved diffraction oscillations which appear damped with respect to the corresponding isotropic He–Ar case. Information on the anisotropy of the interaction is indirectly obtained from the damping of the diffraction oscillations within the framework of the infinite-order-sudden (IOS) approximation. While large discrepancies, within the same scheme of analysis, are found with respect to anisotropy estimates from similar experiments, but performed at a lower resolution, good agreement is observed with respect to those obtained for He–O2 and He–N2 from state-to-state rotationally inelastic DCS measurements. Potential energy surfaces (PES) are derived for all systems by also simultaneously fitting absolute total integral cross sections and second virial coefficient data. Comparisons are made with previous both empirical and theoretical potentials, which also have been obtained from or tested against experimental bulk and scattering properties within the IOS approximation. The derived He–O2 surface is found to be in good agreement with recent results. For He–N2 we propose an empirical PES which predicts several independent scattering and bulk data. For He–NO the surface obtained is an improvement with respect to that previously proposed.