Soft X-ray spectroscopies are powerful tools for probing the local electronic and molecular orbital structures of materials in different phases and various environments. While modern spectroscopic tools using soft X-ray synchrotron photons perspicuously reveal the molecular orbital (MO) structure in detail, structures remain widely unknown in the liquid phase since many of these techniques could only be applied to solutions very recently. Furthermore, the interactions and dynamics of molecules in the liquid phase are especially complicated compared to those in gas and solid phases and thereby impede the understanding of functional materials in solution. This review presents recent developments using soft X-ray radiation for probing the electronic structure of ions and molecules in solution. The presented X-ray absorption, emission, and photo-electron spectroscopy studies exhibit the powerful contributions of soft X-ray liquid spectroscopies in the last few years.
