Ultraviolet high resolution electron energy loss spectroscopy of CO on Pt(110) and benzene on Pt(110)

Recently there has been some controversy about how CO and benzene adsorb on platinum. With CO, there is disagreement over whether there is back donati on of electrons from the metal to the CO 2 pi* orbital. With benzene, there is disagreement, over whether benzene adsorbs in a distorted state. In thi s article we use a standard high resolution electron energy loss (HREELS) s pectrometer with modified electronics to measure the equivalent of a ultrav iolet (UV) spectrum for two different systems: CO on Pt(110) and benzene on Pt(110) and benzene on Pt(110). In the case of CO, the UV spectrum shows p eaks at 5.6 and 8.2 eV that may shift slightly with coverage. By comparison , gas-phase CO shows peaks at 6.2 and 8.3 eV. The difference between the ga s-phase peak positions and those on the surface are indicative of the antib onding orbitals being stabilized, as one would expect from the Blyholder mo del. With benzene we observe two different spectra: a first monolayer spect rum with a bread peak centered at 4.9 eV, and a multilayer spectrum with pe aks at 0.75, 3.82, 4.71,;6.20, and 6.84 eV. The multilayer spectrum matches the spectrum of condensed benzene, while the first monolayer spectrum is q uite different and resembles that of a diene. Together, these results show that UV/HREELS spectroscopy provides useful information about adsorbates on surfaces. (C) 1999 American Vacuum Society. [S0734-2101(99)01804-7].