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Surface Vibrational Spectroscopy Study of Benzene and 2,2,2-Trifluoroacetophenone on Pt(111)

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journal contribution
posted on 14.04.2011, 00:00 by Vincent Demers-Carpentier, Peter H. McBreen
High resolution electron energy loss spectroscopy (HREELS) data for C6H6 and C6D6 on Pt(111) were measured as a function of coverage. The spectra show five additional loss peaks with respect to earlier reports that were used in density functional theory (DFT) calculations of the properties of benzene on Pt(111). The spectra display a strong coverage dependence in the CH stretching region. HREELS and STM data for the adsorption of 2,2,2-trifluoroacetophenone (TFAP) on Pt(111) are used in the analysis of the benzene/Pt(111) system. The TFAP spectra display the same coverage dependence as benzene in the CH stretching region. An analysis of STM images of TFAP dimers shows that their azimuthal orientation is not consistent with the occupation of hcp0 sites. The data for benzene adsorption cannot be explained on the basis of existing density functional theory (DFT) calculations. In particular, the spectra are not consistent with either a C2v symmetry bridge adsorption or a combination of adsorption at C2v symmetry and hcp0 sites. The data provide a benchmark for evaluating the ability of emerging computational approaches to predict the chemisorption properties of strongly chemisorbed aromatics. The data for both benzene and TFAP are of relevance to the asymmetric hydrogenation of ketones on chirally modified Pt catalysts.