Sum-frequency spectroscopic studies of ice interfaces

Sum-frequency vibrational spectroscopy was used to study the (0001) surface of hexagonal ice ${(I}_{h})$ in contact with: air, a hydrophobic substrate, and a hydrophilic substrate. The spectra in the O-H stretch frequency range were obtained at various temperatures. For the air/ice interface, the degree of orientational order of the dangling OH bonds at the surface was measured as a function of temperature. Surface disordering appears to set in around 200 K and increases dramatically with temperature, which is a strong indication of the presence of surface melting of ice. For the hydrophobic and hydrophilic ice interfaces, a similar temperature dependence of the hydrogen-bonded OH stretch peak was observed. The free OH stretch mode, however, appears to be different from that of the air/ice interface due to the interactions with substrates at the interfaces.