High resolution X-ray emission spectroscopy of liquid water: The observation of two structural motifs

We observe two distinct, narrow lone-pair derived peaks in high-resolution X-ray emission spectra (XES) of liquid water, which we assign respectively to tetrahedral and strongly distorted hydrogen-bonded species. We estimate a 2:1 ratio between distorted and tetrahedral species at room temperature and discuss what this implies in connection to a previous, much debated X-ray absorption spectroscopy (XAS) study and in terms of liquid water structure.