Theoretical and computational approaches to describing vibrational spectroscopy of water: bulk liquid, the liquid/vapor interface, and ice Ih

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James Skinner of the University of Wisconsin, Madison is supported by an award from the Theory, Models and Computational Methods program in the Chemistry Division to develop theoretical and computational approaches that describe the vibrational spectroscopy of water in the bulk liquid, the liquid/vapor interface, and ice. Vibrational spectroscopy experiments include frequency-domain infrared, Raman, and sum-frequency-generation measurements, as well as very recent ultrafast time-domain pump-probe or echo studies. The PI and his research group develop theoretical and computational models for the interpretation of these experimental probes, with a focus on obtaining a molecular-level understanding of the structural and dynamical properties of water in its various phases. The PI and his coworkers are developing theoretical and computational models to tackle three scientific problems of current interest. The first involves vibrational energy transfer in liquid mixtures of water and heavy water, as measured by pump probe rotational anisotropy experiments. The second involves the structure and dynamics of water at the liquid/vapor interface, as probed by phase-sensitive or heterodyne detected vibrational sum-frequency spectroscopy. The third involves the nature of vibrational eigenstates in ice as measured by Raman and infrared spectra of single crystal and polycrystalline samples. The goal is to develop unified theoretical models and approaches that are applicable to all variants of vibrational spectroscopy, to compare with experiment, and then to provide molecular-level understanding.Water is an important substance, in each of its gas, liquid, or solid phases, and as a solvent. Despite the simplicity of the water molecule itself, the properties of liquid water, ice, and aqueous solutions are complex, and a complete understanding is still not at hand. Vibrational spectroscopy plays an important role in elucidating the structure and dynamics of water in its condensed phases, because the transition frequency of a local OH stretch vibration is exquisitely sensitive to its hydrogen-bonding environment. Water plays an important role in diverse fields from biology, to earth and atmospheric sciences. The PI has developed an outreach program involving web seminars on water directed to high school teachers, and a traveling road show on water for middle and high school science classes in the Madison area.