Structural analysis of Pt(111)c(√3x5)rect.-CO using photoelectron diffraction

Core level shift scanned-energy mode photoelectron diffraction using the two distinct components of the C 1s emission has been used to determine the structure of the Pt(111)c(root 3 x 5)rect.-CO phase formed by 0.6 ML of adsorbed CO. The results confirm earlier assignments of these components to CO in atop and bridging sites, further confirm that the best structural model involves a 2:1 occupation ratio of these two sites, and provides quantitative structural parameter values. In particular the Pt-C chemisorption bondlengths for the atop and bridging sites are, respectively, 1.86 +/- 0.02 angstrom and 2.02 +/- 0.04 angstrom. These values are closely similar to those found in the 0.5 ML coverage c(4 x 2) phase, involving an atop:bridge occupation ratio of 1:1, obtained in earlier quantitative low energy electron diffraction studies. The results also indicate a clear tilt of the molecular axis of atop CO species in this compression phase, consistent with the finding of an earlier electron-stimulated desorption ion angular distribution investigation. (c) 2006 Elsevier B.V. All rights reserved.