NON-DIPOLE CONTRIBUTIONS AND THE CURVED-WAVE APPROXIMATION FOR SURFACE ELECTRON-ENERGY LOSS FINE-STRUCTURE SPECTRA ABOVE THE N2,3 EDGE OF POLYCRYSTALLINE PALLADIUM

Surface electron energy loss fine structure experiments above the N2,3 edge of polycrystalline Pd have been performed in order to study the applicability of the dipole approximation and the plane-wave-approximation for this system. Strong quadrupole contributions have been determined, which cannot be neglected. Furthermore, the curved-wave approximation rather than the plane-wave approximation has to be used for the calculations of the backscattering phase shifts and the backscattering amplitudes. The use of the plane-wave approximation leads to wrong next-nearest-neighbour distances.