Observation of X-ray resonant Raman spectra and transition to resonant fluorescence

The first observation of X-ray Raman spectra of transition metal compounds is reported on copper, cuprous oxide, and cupric oxide in resonant, pre-resonant as well as non-resonant conditions. In the non-resonant condition the spectra are, unlike fluorescence X-ray, characteristic of each compound. Upon approaching the resonant condition a smooth and continuous transition from Raman spectra to K fluorescence doublet of copper is observed. The excitation energy dependence of the spectra can be reproduced quite well by a simple calculation employing second-order perturbation theory.