The water molecule is the one most essential to our existence. Despite its deceptively simple form, it shows a most complex and rich behavior when it condenses to either a solid or a liquid. Ever since Ršntgen suggested in 1892 that water in its liquid phase consists of two distinct types of coexisting liquids (Ršntgen W.C., Ann. Phys. 45, 91 (1892)), debates have regularly surfaced as to whether water should be regarded as a uniform continuum of local structures or as a mixture of structurally different but intertwined components. In recent years, the latter point of view has gained support from studies of supercooled water where polyamorphism has been shown to exist between a low-density and high-density form differing in local structure from each other.
In this talk I will discuss how our group has contributed to this ongoing debate. It started with the pioneering application on synchrotron x-ray absorption spectroscopy on liquid water in 2004 (Wernet et al., Science 304, 994-999 (2004)), which made an explosive impact on the liquid water community, and has most recently lead to a coherent interpretation of results from x-ray emission and absorption spectroscopies together with small-angle x-ray scattering in terms of a two-component model for liquid water (Huang et al., 106, 15214-15218 (2009)). During the period between these two milestones, our group has worked on extracting structural information from x-ray and neutron diffraction, IR/Raman vibrational spectroscopy and extended x-ray absorption fine-structure (EXAFS), to see how each structural probe contributes to the bigger picture.
I will discuss how the different techniques provide complementary
information on the structure of liquid water, and mention the methods we have devised to compare, contrast and attempt to unify the structural information from each technique."