Hard X-ray photon-in photon-out spectroscopy

Spectroscopic techniques to study the electron configuration and local coordination of a central atom by detecting inner-shell radiative decays following photoexcitation using hard X-rays are presented. The experimental setup requires an X-ray spectrometer based on perfect crystal Bragg optics. The possibilities arising from non-resonant and resonant X-ray emission spectroscopy are discussed when the instrumental energy broadenings of the primary (beamline) monochromator and the crystal spectrometer for X-ray emission detection are on the order of the core hole lifetimes of the intermediate and final electronic states. The small energy bandwidth in the emission detection yields line-sharpened absorption features. In transition metal compounds, electron–electron interactions as well as orbital splittings and fractional population can be revealed. Combination with EXAFS spectroscopy enables to extend the k-range beyond unwanted absorption edges in dilute samples that limit the EXAFS range in conventional absorption spectroscopy.