EXAFS for liquids

Extended x-ray absorption fine structure (EXAFS) spectroscopy exploits the quantum interference resulting from the scattering of a photoelectron, gene rated by the excitation of a core level, by the potential of the surroundin g atoms. From the interference pattern it is possible to determine the dist ance and average distribution of the nearest neighbours from the photoabsor bing atomic species. This spectroscopy therefore provides a unique site-sel ective local structural probe in condensed matter which is ideal for invest igating the average environment of specific elements in a liquid. In the la st 20 years we have seen substantial developments in the experimental techn iques which nowadays allow scientists to perform EXAFS experiments under ex treme conditions of high pressure and temperature that were not even concei vable just a few years ago. These techniques have been applied to the inves tigations of metals, semiconductors, molecular fluids and solutions, as a f unction of pressure and temperature and through phase transitions, attracti ng a wide scientific community towards this spectroscopy. The complete unde rstanding of the x-ray absorption signal is however a challenging theoretic al problem involving the many-electron response of the system. Our current theoretical framework for the interpretation of the EXAFS spectra is based on the solution of an effective one-electron problem. This theory is nevert heless accurate enough to be used in a quantitative data analysis able to r etrieve valuable structural information.