X-ray Raman spectroscopy at the oxygenKedge of water and ice: Implications on local structure models

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Abstract
The oxygen K edge of water and ice has been recorded with a resolution of 1 eV using x-ray Raman spectroscopy at 10 keV. The improved resolution allows for a clear observation of the strong pre-edge intensity in the liquid water spectrum. This is an independent experimental confirmation of this feature, which was recently detected by high-resolution soft-x-ray absorption spectroscopy and identified as a fingerprint of strongly asymmetric local configurations of the water molecules. The pre-edge peak as observed here with the truly bulk-sensitive x-ray Raman technique demonstrates that these configurations dominate the bulk of the liquid. Comparison with the K edge of ice gives an experimental limit on the fraction of fully coordinated waters in the liquid.