Extended Pi-Sigma tilde orbital model for CO adsorption on Pt and Ru*

Several discrepencies between the predicted Blyholder-type adsobtion models and experimental, as well as DFT calculated infared spectra have been addressed for atop CO on Pt in contrast to Ru. This model correlates increased Near Edge X-Ray Absorbtion Fine Structure intensity as the result of a sub-eV downshift from CO on Ru compared to CO on Pt thereby forming a weaker C-O bond. The model accounts for the hybrid orbitals electron transfer between the CO - metal bonds while taking in to consideration the orbital polarization within the CO itself. The charge redistribution of the s-tilde orbitals and reduced charge donation from CO to the surface results in a weaker internal CO bond upon Ru relative to Pt. The extended Pi-Sigma model explains why atop C-O stretching frequencies do not correlate with carbon p-type vacancies.