Distortions of x-ray absorption spectra measured with fluorescence yield

The 2p X-ray absorption spectra of 3d transition metal compounds measured with fluorescene yield (FY) appear disorted. It is shown that this disortion is intrinsic to FY detection and not due to self-absorption. It results from the final-state dependent variation of the fluorescene decay, which is more than 400%. The Auger decay is also final-state dependent but the variation is only 25%. In the approximation that the final states do not interfere with each other (which is shown to be approximately correct for Ni^2+), the FY spectral shape identifies with the X-ray absorption spectrum multiplied with its symmetry-dependent fluorescence decay. Results are given for the nickel 2p edge of Cs[NiCr(CN)6] * 2H2O measured synchronously with FY and electron yield