The radial distribution function probed by X-ray absorption spectroscopy

Structural information on the pair distribution function g 2 (r) for single-component disordered systems is usually obtained from the experimental structure factor S(k) measured by diffraction techniques. Complementary short-range information can be provided by the analysis of the extended X-ray absorption fine structure chi (k) associated with a certain X-ray absorption edge. The intrinsic differences in the nature of the chi (k) and S(k) signals are discussed and particular effort is devoted to connecting the chi (k) signal with usual quantities familiar to the distribution function theory in disordered matter. An example of the short-range chi (k) sensitivity is presented showing signals associated with g 2 (r) functions of liquid Cu at 1150 degrees C and 1300 degrees C. The necessity to fit realistic g 2 (r) models to EXAFS spectra satisfying both long-distance behaviour and the compressibility sum rule is emphasized. A method to combine these constraints and previous information on g 2 (r) with available chi (k) data is proposed and applied to recent EXAFS data on liquid palladium.