Vibrational studies that selectively probe molecular structure at CCl4/H2O and hydrocarbon/H2O interfaces show that the hydrogen bonding between adjacent water molecules at these interfaces is weak, in contrast to generally accepted models of water next to fluid hydrophobic surfaces that suggest strong hydrogen bonding. However, interactions between these water molecules and the organic phase result in substantial orientation of these weakly hydrogen-bonded water molecules in the interfacial region. The results have important implications for understanding water adjacent to hydrophobic surfaces and the penetration of water into hydrophobic phases.

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The average dipole moment of a water molecule in the condensed phase is enhanced by around 40 percent relative to that of an isolated monomer. This enhancement results from the large polarization caused by the electric field induced by surrounding monomers. A quantitative molecular description of this polarization is essential for modeling aqueous solvation phenomena. This combined theoretical and experimental study of dipole moments in small water clusters provides such a description and also gives insights into the structure of liquid water.

Measurement of the far-infrared vibration-rotation tunneling spectrum of the perdeuterated water tetramer is described. Precisely determined rotational constants and relative intensity measurements indicate a cyclic quasi-planar minimum energy structure, which is in agreement with recent ab initio calculations. The O-O separation deduced from the data indicates a rapid exponential convergence to the ordered bulk value with increasing cluster size. Observed quantum tunneling splittings are interpreted in terms of hydrogen bond rearrangements connecting two degenerate structures.

Far-infrared laser vibration-rotation tunneling spectroscopy was used to measure an intermolecular vibration (81.1 91 98 wave numbers) of the isolated water (D,O) pentamer. Rotational analysis supports the chiral, slightly puckered ring structure predicted by theory. The experimentally deduced interoxygen separations for the water clusters up to the pentamer showed exponential convergence toward the corresponding distance in bulk phase water.