Structure of Physisorbed Molecules on an Oxide Surface from Potential Calculations and Dynamical Low-Energy Electron Diffraction Analysis: Acetylene on MgO(100)

Semiempirical potential calculations have been combined with a dynamical low-energy electron diffraction analysis to determine the complete structure of molecules physisorbed on an oxide surface, namely, acetylene (C₂{H}₂$) adsorbed on MgO(100) at $T{{0ex}{0ex}}={{0ex}{0ex}}88K$. This allows determination of the adsorption sites and the molecule-molecule and molecule-substrate distances. The results are consistent with molecules that lie almost parallel to the surface in a herringbone structure. Neither molecule nor substrate exhibits significant distortions, due to the weak physisorption.