LOW-ENERGY HE-4(+) SCATTERING FROM DEUTERIUM ADSORBED ON STEPPED PD(331)

We have taken angle-resolved data for the scattering of low-energy (< 1 keV) He-4(+) from deuterium adsorbed on a stepped Pd(331) surface. T he impact geometry was ''up the staircase,'' i.e. the He-4(+) beam was perpendicular to and directly incident onto the unshadowed [011] Pd l edge atoms. A strong quasielastic scattering signal of He-4(+) from D (He-4(+)/D) was observed at a forward-scattering angle of theta = 25 d egrees and an incidence angle of alpha = 76 degrees from the (331) nor mal. The results agree with shadow-cone calculations of scattering fir st from Pd ledge atoms followed by a second event, He-4(+)/D. The resu ltant adsorption geometry shows D to reside in the quasi-threefold led ge site on the surface directly above the bulk fee octahedral void. Th ese results are consistent with the previous He-4(+) scattering study of the geometrically related Pd(110)-D(ads) system.