We provide evidence for particle size effects and shed light on the structure-activity relationship for the Cu-on-ZnO(0 0 0 1) system. The energy transfer processes governing the adsorption of CO depend distinctly on the morphology of the metal-onmetal oxide system as evident by impact energy dependent variations in the shape of the coverage dependent adsorption probabilities. (c) 2005 Elsevier B.V. All rights reserved.