X-ray Absorption Spectroscopy investigations of disordered matter

X-ray Absorption Spectroscopy (XAS) is known to be an ideal technique for investigating matter lacking crystalline ordering. This work reports about present methods used for investigating disordered matter, discussing data-analysis and simulations strategies as well as several experimental techniques with applications. The current approach based on the comparison among multiple-scattering simulations associated with the n-body distribution functions and EXAFS (Extended X-ray Absorption Fine Structure) experimental data, including application of Reverse Monte Carlo methods, is discussed. Several studies of amorphous and liquid systems are presented, showing the potential of XAS in answering some important questions related to preferred local symmetries in liquid systems and presence of polymorphism in glasses and liquids. Experiments are presented discussing also the advances related to the performance of high-pressure and high-temperature experiments in disordered systems, highlighting the importance of combining XAS, x-ray diffraction and suitable diagnostics. XAS ability in measuring phase transitions and structure in undercooled metastable liquids is discussed. New possibilities offered by EXAFS measurements of light elements using inelastic scattering (x-ray Raman) are presented discussing the notable example of liquid water. Mention to new time-resolved applications at synchrotrons and free-electron lasers is also given.