Intermolecular interactions in liquids revealed by soft X-ray absorption spectroscopy

Soft X-ray absorption spectroscopy (XAS) is an effective method to perform element-selective analyses of liquid structures. In this review, we explain a precise liquid thickness control method for XAS of liquid samples in transmission mode and propose two theoretical approaches for analyzing liquid structures with the inner-shell quantum chemical calculations: One approach is that the liquid structures are determined by the inner-shell calculations of model structures. The hydrogen bond networks in aqueous dimethyl sulfoxide solutions were investigated by the oxygen K-edge XAS measurements with this theoretical approach. The other approach is the summation of the inner-shell spectra of small liquid structures including structural deviations. The carbon K-edge XAS spectrum of liquid ethanol was well reproduced by this theoretical approach. Future aspects of the XAS measurement methods of liquid samples to perform operando observations of several chemical phenomena in solutions are also discussed. (author)