The anisotropic interaction of He-C2H2 from differential scattering experiments

The anisotropic potential energy surface of He–C2H2 is determined by analyzing total differential cross sections measured at E=71.3 meV and differential energy loss spectra obtained at two energies, E=102.9 and 62.0 meV. Calculations are carried out using infinite-order-sudden, coupled states, and close coupling methods. The data evaluation clearly demonstrates that the experimental results are much better reproduced by a spindle-shaped contour in the repulsive potential than by the more usual hard ellipsoidal shape. This change also explains the unusually small damping of the diffraction oscillations in the total differential cross section.