Theoretical study of the CO adsorption on the (100) surface of the face-centered cubic d-block transition metals

The interaction of a CO molecule with the (100) surface of the fee d-block transition metals is analyzed by the topology of the Laplacian of the electronic charge density -del(2)rho. This analysis shows that the atomic graph for the top atoms is an octahedron that exposes, outside the (100) surface, a vertex V-top with a local maximum of charge, and four faces F-top with a local minimum. The corresponding graph for the second-layer atoms is also an octahedron that exhibits a vertex V-sec outside the surface. Atomic graphs for the CO molecule show that the carbon atom has a non-bonded vertex C-nb, and a torus C-torus of charge depletion perpendicular to the C-O bond direction. Laplacian topology predicts CO perpendicular orientation in bridge- or top-sites. The bridge-site involves attractive interactions with two atoms of the surface: face (metal top atom)-vertex (C atom)-face (metal top atom). The top-site involves the attractive interaction vertex (C atom)-face (metal top atom). Attractive interaction between the surface and only one atom of the CO molecule rules out dissociation and predicts molecular adsorption. (C) 1999 Elsevier Science B.V. All rights reserved.