Adsorbate-induced changes in the structure of amorphous thin films of ice

The effect of adsorption of thiophene on the infrared spectra of thin amorphous ice films deposited on Pt(111) is studied using reflection-absorption infrared spectroscopy (RAIRS). The changes within the RAIR spectra in the range of the O-H-stretching band system upon adsorption depend on the structure of the ice films and the temperature at which the thiophene is deposited. Preferred binding at the ice surface to sites that are most likely identical with dangling-H groups occurs only if adsorbate mobility is sufficiently high. Otherwise, random film growth is observed, i.e., formation of multilayer islands before the first layer of thiophene on ice is completed. The adsorbate-induced changes within the O-H-stretching band system of the ice films are different for these two situations. Binding to dangling-H sites is shown to influence more than the uppermost layer of the ice, whereas random deposition has an effect only on surface vibrational modes.