Rainbow scattering under axial surface channeling

For scattering of fast atoms from metal surfaces under axial channeling conditions we observe pronounced peaks in the angular distributions of scattered projectiles which can be interpreted in terms of rainbow scattering. These structures are closely related to the interaction potentials which can be deduced from the data with good precision. We have scattered He, Ne, and N atoms with keV energies from Al(1 1 1), Cu(1 1 1), and Ag(1 1 1) surfaces and compare the observed rainbow structures using different approaches for the interatomic pair potentials. From our analysis we find experimental evidence for an additional contribution to the overall interaction potential for atoms at metal surfaces caused by screening effects in the electron gas in front of the surface. As an example for the relevance of our finding for ion/atom surface collisions, we discuss the widths of angular distributions for projectiles scattered under glancing angles. Incorporation of this contribution to the scattering potential allows us to explain the different behaviour of angular distributions for noble gas and reactive atoms with scattering conditions.