From monomers to ice -: new vibrational characteristics of H2O adsorbed on Pt(111)

H2O adsorption on Pt(1 1 1) was studied by high-resolution electron energy loss spectroscopy over a wide exposure range at 85 K. We conclude that the known loss of the ice multilayer at about 30 meV is due to T-perpendicular to4, the Pt-OH2 translational mode perpendicular to the surface. This new assignment gives rise to a very consistent understanding of the vibrational spectra for thicker ice layers, for the bilayer, and for sub-monolayer coverages. For the bilayer two perpendicular modes are observed at 33 meV for the top H2O molecule and at 16.5 meV for the bottom H2O bonding to the surface Pt atom. For a new low-coverage phase only one TI is found at 15 meV. Following a recent scanning tunneling microscopy result of Morgenstern et al. [1]: the latter is assigned to H2O monomers adsorbed in chains at the Pt(1 1 1) step edges. The newly observed monomer translation mode T-perpendicular to1 at 15 meV can be used as an indicator for small amounts of H2O co-adsorbed within O or OH layers. O 2001 Elsevier Science B.V. All rights reserved.