Scattering of thermal He beams by crossed atomic and molecular beams. V. Anisotropic intermolecular potentials for He+CO₂, N₂O, C₂N₂

Experimentally measured differential cross sections are presented for the interactions of He with the linear molecules CO₂,N₂O, and C₂N₂. These data show pronounced dampening of the diffraction oscillations, and provide an indication that the intermolecular potentials have large anisotropics. Indeed, central-field analyses of the experimental data, even in terms of very flexible models, are shown to be inadequate. However, an anisotropic analysis using the infinite-order sudden approximation yields physically reasonable intermolecular potentials, and provides excellent fits to the scattering data. Neither the spherical averages of these empirical anisotropic potentials, nor the spherically symmetric potentials obtained by the central-field analyses, reproduce the experimental differential cross sections. For He+CO₂, the anisotropic potential is extended to highly repulsive interactions, to which the present data are insensitive, by combining theoretical calculations and measurements of gas-phase bulk properties. Estimates for the reliability of the fitted anisotropic potentials are given, and convenient parametrizations are recommended.