Kinematical rainbow and elastic focusing effects in atom-surface scattering

Abstract

In this work two general anomalous singularity effects in elastic surface diffraction are reported. First, a kinematical rainbow (KR) condition, a special case of the well-known rainbow singularity, is examined and shown to be a two-dimensional counterpart of the glory effect in gas-phase scattering. Second, an elastic focusing (EF) effect is presented as the elastic counterpart of a general effect called inelastic focusing recently observed in the inelastic scattering of He atoms from a NaCl(001) surface. Both effects occur under conditions in which the angular positions of the diffraction channels are degenerate in pairs. In the vicinity of the KR the coupling among diffraction channels is strongly rearranged and noticeable changes in the diffraction pattern intensities are expected, whereas the EF enhances the observed intensity of only the affected diffraction peak. As an illustration of these general phenomena in surface scattering, calculations are presented demonstrating that both of these new effects should be observable for He atom scattering from stepped metal surfaces. ©1999 The American Physical Society.