Geometry of C1-3 oxygenates on ZnO(0001)-Zn

C K-edge near edge X-ray absorption fine structure has been used to identify and determine the orientation of adsorbed species resulting from exposure of ZnO(0 0 0 1)-Zn to CO, CO2, formic acid (HCOOH) and acetone ((CH3)(2)CO). Spectra obtained at 110 K after CO adsorption indicate that the molecule is aligned along the surface normal. Carbonate is also formed after CO exposure, which has the molecular plane almost parallel to the surface. This species is also formed by exposure of the substrate to CO2 at 270 K. Formate created by exposure of the substrate to formic acid at 400 K and annealing to 450 K displays 'magic angle' behaviour, with no preferred orientation. Acetone adsorbs at 310 K in part molecularly and in part dissociatively to form a carbanionic enolate. Annealing this overlayer to 520 K leaves just the enolate, with the CO group lying along the surface normal. This behaviour of ZnO(0 0 0 1)-Zn is consistent with that expected on the basis of recent calculations that predict that the surface is metallic. (C) 2001 Elsevier Science B.V. All rights reserved.