Electronic and vibrational structure in liquid water probed by soft X-ray resonant inelastic scattering and modeling

Recent high-resolution soft X–ray resonant inelastic X-ray scattering technique enables us to distinguish valence electronic structure of water molecules having different hydrogen-bond configurations in the liquid phase. Moreover, in the elastic region, well-separated multiple vibrational structures appear, which corresponds to the internal OH stretch vibration in the ground state. Both the valence band profile and the vibrational energy of OH stretch in the  = 1 state varies with the excitation energy. Connecting the vibrational energy to the conventional Raman spectroscopy, this indicates that water molecules with a particular hydrogen bond configuration can selectively be excited by tuning the excitation energy. Recent state-of-the-art simulation has successfully reproduced the valence band spectra and strongly supported a heterogeneous picture of liquid water with fluctuating patches of high and low density hydrogen bond configurations.