Light Scattering Studies of Supercooled Water (Chemistry)

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Light scattering experiments are planned for supercooled water and aqueous solutions to elucidate the structural mechanisms responsible for thermodynamic anomalies in supercooled water. Raman data obtained from this work will have direct structural information for supercooled water. The OH stretch modes will yield nearest neighbor information including hydrogen bond probability, and mean O-O separation and distribution. The low frequency intermolecular modes will yield information regarding the second neighbor shell wherein the most dramatic structural changes relevant to the supercooled anomalies are thought to occur. The photon correlation spectroscopy measurements will be used to extract effective density correlation lengths due to cooperative behavior between many water molecules. Water's importance on the face of the earth cannot be overstated. This importance stems from two sources: its abundance, and its unique physical and chemical properties. In the past decade it has been found that liquid water is even more unusual in the supercooled regime below zero degrees Centigrade. Here it displays anomalies in its thermodynamic and transport properties which may be approaching a singularity. The key to water is in its hydrogen bonded structure. Raman spectroscopy can give microscopic information regarding structure and dynamics. It can determine the extent of hydrogen bonding, make decisions regarding ice-like or clathrate structures, and give information on both the first neighbor shell and molecular clustering.