Determination of azimuthal orientation with impact scattering? Bithiophene on Ni(110) p(4×1)-S

The p(4 x 1)-S reconstructed Ni(110) surface provides a highly corrugated template for the orientation of molecular adsorbates. Off-specular HREELS clearly shows the preferential azimuthal orientation of the bithiophene molecule on this substrate. However, it is argued that the orientation implied by the application of the impact scattering selection rule in the direction perpendicular to the surface ridges is incorrect. Rather than decreases in intensity in particular scattering geometries due to modes being forbidden, the observed intensity variations with azimuth appear as a result of intensity increases, in particular for out-of-plane modes when the scattering is perpendicular to the molecular plane. (C) 1998 Elsevier Science B.V. All rights reserved.