Hydrogen bonding in the prism face of ice Ih A study via sum frequency generation vibrational spectroscopy.

摘要

The prism face of single crystal ice Ih has been studied using sum frequency vibrational spectroscopy focusing on identification of resonances in the hydrogen-bonded region. Several modes have been observed at about 3400 cm-1; each mode is both polarization and orientation dependent. The polarization capabilities of sum frequency generation (SFG) are used in conjunction with the crystal orientation to characterize three vibrational modes. These modes are assigned to three-coordinated water molecules in the top-half bilayer having different bonding and orientation motifs.;Such mode identification is only possible with the production and use of single crystal ice of very low defect density and of size appropriate for examination using the SFG technique. Production of single crystal ice is often trivialized in the literature. But in reality, large single crystals are very difficult to produce. Design and construction of an apparatus and protocol that can produce large single crystals of ice truly advances the state of the art. An apparatus utilizing the Bridgeman-Stockbarger method of single crystal growth was designed, constructed and optimized for the growth of ice. This design features a software implemented (LabVIEW) Proportional-Integral-Differential (PID) feedback temperature control algorithm. The temperature at the growth interface was controlled to within +/-0.002K even though room temperature variation was ca. +/-2K.;Since the measurement must occur at cryogenic temperature (ca. 130K), the design and construction of a cell that can enclose and isolate the ice sample from ambient conditions is also of critical importance. An air tight, all glass design was chosen that incorporates two fused IR quartz windows to allow for visible and mid-IR transmittance, an oxygen free copper heat sink and a unique ice mounting scheme. The thermal design of the heat sink and ice mount are critical for reaching cryogenic temperatures and insuring the ice sample remains attached to the heat sink as the temperature is lowered.