Water at surfaces: What can we learn from vibrational spectroscopy?

Recent developments in the vibrational spectroscopy of thin films of water adsorbed on well defined metal surfaces under ultra-high vacuum (UHV) conditions will be discussed. New results will be presented for H2O and D2O adsorbed on Cu(110), measured using grazing incidence reflection-absorption infrared spectroscopy (RAIRS). These will be discussed in context with previous high-resolution electron energy loss spectroscopy (HREELS) measurements of H2O on Pd(110). Both of these results are typical of measurements from other laboratories. Particular attention will be paid to the O-H stretching region of the spectrum. A detailed examination of this region of the spectrum is used to study the amorphous to crystalline phase transition in thin films, the temperature dependence of the sticking coefficient of water, and the structure of the first one or two layers of water directly at the solid interface. The spectroscopic signature observed for very thin films is found to be consistently different from that of crystalline ice, and the possible reasons for this difference are discussed.