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.
Water is one of the most important substances on earth. It is in the atmosphere, the oceans, lakes, and rivers, in the polar ice caps, and in our bodies. Thus, understanding the role of water is important for many sciences and technologies, including biology and medicine. The water molecule itself is very simple: two atoms of hydrogen and one of oxygen, joined together with two chemical bonds. When many molecules interact, however, as they do in the liquid or solid states, or in biological cells, the behavior becomes rich and complex. Many researches have tried to model water at the molecular level for many years. Trying to develop a more sophisticated model that can be used for simulation in a variety of different physical applications was one of our goals. Our new model takes into account simultaneous interactions among three molecules, and has been shown to be quite successful. One way to measure the properties of water is through spectroscopy, which involves the absorption of light. New experimental techniques involving infrared lasers have recently been developed. In order to interpret these experiments, we need new techniques for calculating spectroscopic observables. The other main goal of our research has been to develop and apply these new theoretical techniques. Some of the outcomes of our work have been a better understanding of the structure and dynamics at the water liquid/vapor interface, the relationship between hydrogen bonding and infrared spectroscopy, and the nature of disorder in crystalline and amorphous ice.
