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

In this letter we present a chemical shift photoelectron diffraction (CS-PE D) study of the c(4 x 2) phase of CO on Pt(111), in which two molecular spe cies are present. The angular dependence of both chemically shifted Cls cor e levels was independently determined in a high resolution photoemission ex periment. By means of a full multiple scattering analysis, the local struct ure 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 p osition gives good agreement with the experimental data, in accord with pre vious structural studies of this system. Our result highlights the capabili ties of CS-PED for the study of complex adsorption systems where the same m olecule occupies different adsorption sites. (C) 2000 Elsevier Science B.V. All rights reserved.