X-ray spectroscopy studies of water and aqueous solutions

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Anders Nilsson of Stanford University is supported by the Experimental Physical Chemistry Program to use x-ray absorption spectroscopy (XAS) and x-ray Raman scattering (XRS) to examine liquid water and aqueous solutions. Recent studies of water based on XAS and XRS have suggested that liquid water has on average only two strong hydrogen bonds per molecule rather than ~3.5 as is commonly believed. If confirmed, this would dramatically change the current thinking about the structure of water and its role in the many processes in which it is involved. The techniques to be employed here are based on the use of inner shell electrons from the absorbing/scattering oxygen atom to probe the unoccupied valence electron structure, which depends in detail on the molecular arrangements. An important aspect of this project is to use a combination of experiments and density functional theory (DFT) calculations to integrate available experimental molecular data on water. From such a combination of experiment and theory, the local hydrogen-bonding coordination around water molecules can be probed with sensitivity to both bond elongations and angle distortions. It is hoped that this new unique information regarding the structure of water under different thermodynamic conditions will enable understanding of the microscopic origin of water's many unusual properties. Similarly, the influence of ions on the water hydrogen-bonding network in aqueous solutions is critical to unraveling the role of water in chemical and biological processes.Water is the key compound for our existence on this planet, and it is involved in nearly all biological, geological, and chemical processes. It has been studied intensively for hundreds of years but is still puzzling scientists. New knowledge about the hydrogen-bonded network structure in water is essential to understand its many unusual chemical and physical properties. Water research is expected to have a broad impact on general interest in chemistry in the media, general public, and for science high school teachers.