Rotationally inelastic collisions studied by using model potential energy surfaces. 1. Polarization and rainbow effects and their dependence on the attractive well

Scattering calculations for rotational energy transfer on model potential energy surfaces have been used to elucidate the direct influence of potential energy surface topography on the polarization of integral cross sections, and on differential cross sections. For purely repulsive surfaces, integral cross section polarization data are sensitive to the potential energy contour eccentricity, just as the differential cross sections are. For scattering on substantially attractive surfaces, it is shown how the two types of data provide complementary information. The polarization data probe the angular orientation of the absolute attractive minimum, and are largely independent of the range of attraction. Rainbow features in the state-to-state differential cross sections should allow the attractive and repulsive parts of the intermolecular potential energy surface to be probed fairly independently. Mechanisms for energy transfer on the model potential energy surfaces are discussed, particularly as to how they differ for surfaces having T-shaped or collinear equilibrium geometries. The qualitative conclusions reached here are shown by way of specific examples to be independent of our use of classical mechanics.