Liquid water structure from X-ray spectroscopy and simulations

This paper deals with insights into the structure of liquid water obtained from X-ray spectroscopies, diffraction, small-angle scattering and molecular dynamics simulations. From a large collaborative effort by experimentalists and theoreticians to understand liquid water, a picture consistent with thermodynamic models proposing a transition between high-density and low-density liquid states in the supercooled region has evolved. Through the observation of two coexisting structural motifs in the X-ray spectroscopies even in ambient water, a connection is established between the anomalous properties in the supercooled regime to the behavior of water at higher temperatures. Diffraction data are shown to be inconclusive regarding the local structures found in the liquid, but experimental extended X-ray absorption fine structure data are shown to contain new information regarding the hydrogen bonding network. Lastly, small-angle X-ray scattering data showing an increasing correlation length upon supercooling suggest, combined with simulations, that a liquid-liquid critical point is present in the deeply supercooled regime.