STRUCTURE OF PHYSISORBED MOLECULES ON AN OXIDE SURFACE FROM POTENTIALCALCULATIONS AND DYNAMICAL LOW-ENERGY-ELECTRON DIFFRACTION ANALYSIS -ACETYLENE ON MGO(100)

Semiempirical potential calculations have been combined with a dynamic al low-energy electron diffraction analysis to determine the complete structure of molecules physisorbed on an oxide surface, namely, acetyl ene (C2H2) adsorbed on MgO(100) at T = 88 K. This allows determination of the adsorption sites and the molecule-molecule and molecule-substr ate distances. The results are consistent with molecules that lie almo st parallel to the surface in a herringbone structure. Neither molecul e nor substrate exhibits significant distortions, due to the weak phys isorption.