Structural determination of molecules adsorbed in different sites by means of chemical shift photoelectron diffraction: c(4 x 2)-CO on Pt(111)

In this letter we present a chemical shift photoelectron diffraction (CS-PED) study of the c(4 x 2) phase of CO on Pt(111), in which two molecular species are present. The angular dependence of both chemically shifted Cls core levels was independently determined in a high resolution photoemission experiment. By means of a full multiple scattering analysis, the local structure around each of the two CO species has been quantitatively evaluated. A configuration with half of the CO molecules on top and half in the bridge position gives good agreement with the experimental data, in accord with previous structural studies of this system. Our result highlights the capabilities of CS-PED for the study of complex adsorption systems where the same molecule occupies different adsorption sites. (C) 2000 Elsevier Science B.V. All rights reserved.