Interactions between adsorbed molecules

We review recent work aimed at measuring and understanding interactions between adsorbed atoms and molecules separated by a few surface unit cells. At these distances, poorly understood phenomena associated with substrate mediation play a major role in determining both the sign and the magnitude of the lateral interactions. Our limited fundamental understanding of such interactions leads to limited predictive power in a broad range of important surface kinetic and thermodynamic phenomena, ranging from kinetic compensation to ensemble effects in catalytic reactions. (C) 1998 Elsevier Science B.V.