Selective adsorption in /sup 4/He-MgO scattering

Helium scattering data from an in situ cleaved, oxygen-treated, room-temperature surface of MgO(100) are reported. The sharpness of the selective adsorption line shapes as well as the strength of the scattered beams indicate an improvement over previous studies on air-cleaved surfaces. Selective adsorption line shapes in azimuthal scans of the specular intensity at many closely spaced angles of incidence are presented. Analysis of the resonances at several reciprocal lattice vectors yielded binding energies of 5.52, 2.57, 1.16, 0.54, and 0.26 meV.