AVS 52nd International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM2
Strategies for DFT Modeling of Experimental Surface Vibrational Modes

Tuesday, November 1, 2005, 8:40 am, Room 202

Session: Vibrational Spectroscopy of Surfaces
Presenter: P. Uvdal, Lund University, Sweden
Authors: P. Uvdal, Lund University, Sweden
M.P. Andersson, Technical University of Denmark
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We have explored and developed electronic structure calculations as a tool for the interpretation of experimental vibrational spectra of surface adsorbates. By combining high sensitive surface infrared spectroscopy and density functional calculations details in the spectra, beyond the harmonic level, can be analyzed. These details allow us to extract new information about the physical properties of adsorbed molecules, information not available using the harmonic or normal mode approximation. For instance the C-H stretch region of organic adsorbates contains often more than 50% of the informational content of the vibrational spectrum. Any proper assignment of this region can, however, not be done at the normal mode level. It requires a treatment, which includes anharmonic coupling between fundamental C-H stretch modes and binary/overtone modes of CH3 and CH2 bending modes. This complicates the comparison between calculations and experiments. Base on the concept of spectral moment or intensity weight average one can however obtain the unperturbed frequency of a vibrational mode, e.g. the C-H stretch mode in methoxy. This frequency can then directly be compared to the frequency determined by calculations in the absence of anharmonic coupling between fundamental and binary/overtone modes. This new concept is discussed and related to our recently determined new scaling factor for harmonic vibrational frequencies using the B3LYP density functional method with the triplezeta basis set 6-311+G(d,p)@footnote 1@. @FootnoteText@ @footnote 1@M. P. Andersson and P. Uvdal, J. Phys. Chem. A 109, 2937 (2005).