Employing high energy resolution medium energy ion scattering we have
identified the direction in which adsorbed oxygen sits relative to the
surface Al atoms on the Al(111) surface. Using energy differences ass
ociated with the deflection of the ions by oxygen atoms after scatteri
ng from the surface layer Al (multiple scattering) the oxygen site has
been identified as a surface three-fold hollow site directly above th
ird layer Al atoms and 0.58 angstrom above the surface.