Optical interaction potentials from differential cross section measurements at thermal energies. I. He(23S)+Ar

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Abstract
Differential cross sections for He(23S)+Ar have been measured in the relative kinetic energy range from 20 to 480 meV. At low kinetic energies the small-angle oscillations have been resolved, so that it was possible to derive an accurate complex or optical interaction potential. The velocity dependence of the ionization and total cross sections calculated from this optical potential is in good agreement with experimental results. Orbiting resonances are predicted at low velocities. The derived potential is unusually soft for large internuclear distances, where the argon atom penetrates only the diffuse He(2s) orbital. The repulsion becomes much harder when the argon atom starts to overlap the He(1s) orbital.