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

• DOI: 10.1016/j.cplett.2008.04.077
• Publication Date: 2008-04-24T14:22:02Z
• Authors: T. Tokushima; Y. Harada; O. Takahashi; Y. Senba; H. Ohashi; L.G.M. Pettersson; A. Nilsson; S. Shin
• Keywords: 02 engineering and technology; 0210 nano-technology

The structure of liquid water is presently under intense debate. We summarize the historical development of the present description of water and the controversy surrounding the X-ray absorption spectroscopy (XAS) study of Wernet et al. [Ph. Wernet et al., Science 304 (2004) 995]. In order to provide further insight into the connection between X-ray spectroscopy and the structure of the hydrogen bonding network, we report new data comprising high resolution oxygen K-edge X-ray emission spectra (XES) of liquid water. We observe two distinct narrow lone-pair derived peaks, assigned, respectively, to tetrahedral and strongly distorted hydrogen-bonded species; the assignment is based on comparison with ice and gas phase spectra, temperature dependent measurements, excitation energy dependence and theoretical simulations. We estimate a 2:1 ratio between distorted and tetrahedral species at room temperature and discuss what this implies in connection to the previous XAS study and in terms of liquid water structure.