Surface and bulk contributions to sum-frequency vibrational spectroscopy of single crystalline ice

We study the bulk and surface contributions to the sum-frequency vibrational spectroscopy (SFVS) of ice I_h(0001) interfaces in the bonded OH stretching band at 223K. Using phase-sensitive SFVS with selected polarization combination and beam geometry, a pure electric quadrupole SF spectrum from bulk ice was obtained. Base on analysis of selection rule, an electric quadruple sub-band near 3120 cm^-1 originated from the bulk was found to constitute large portion in the reflected SF spectrum of vapor/ice interface. Via modification of ice surface by absorption of a monolayer of ethanol, the SF vibrational spectrum was significantly reduced at ~3170 cm^-1, suggesting the surface is also important in the ice SF spectrum. These results not only reveal the importance of bulk contribution in SFVS spectrum of ice, but pave the way for investigation of ice surface, e.g. surface premelting, in practical environments.