Sum Frequency Spectroscopic Observation of Aluminol and Water Species


Sum frequency spectroscopy is an interface selective technique which allows us to determine the chemical composition and geometric structure of a surface at the molecular level We apply the technique to in situ studies of model mineral surfaces in water. At the sapphire(001)/water interface, we observe different aluminol species. Also the interaction of the different species with the adjacent water molecules can be observed (polar water orientation and type of binding). The spectral band widths for the different functional species provide information on the number of hydrogen bonds with neighbouring water molecules and thus information on their hydrophobic or hydrophilic character. The results are compared with the results from Monte Carlo simulations (TU Munich) and ab initio quantum chemical calculations (KIT Karlsruhe) of the same interface. The quantitative understanding of such interfaces at the molecular level is important for the reliable modelling of their sorption capability and the transport of contaminants such as radionuclides in the aquifer.