New high-energy approximation for x-ray-absorption near-edge structure

Spherical-wave corrections in x-ray-absorption fine structure (XAFS) are incorporated using a novel high-energy approximation which replaces the plane-wave approximation and is found to be in excellent agreement all the way to the absorption edge. The single-scattering theory of XAFS is recovered in terms of distance-dependent backscattering amplitudes. Application to the $K$-shell XAFS of Cu yields results in close agreement with the corresponding exact treatment. Multiple-scattering contributions in XAFS and spherical-wave corrections in angle-resolved photoemission are treated similarly.