ATOMIC BACKGROUND IN X-RAY-ABSORPTION SPECTRA OF 5TH-PERIOD ELEMENTS - EVIDENCE FOR DOUBLE-ELECTRON EXCITATION EDGES

A systematic x-ray absorption study to detect atomic background featur es at the K edges of fifth-period elements is reported. Samples of MoC x (Z = 42) and pure Rh (Z = 45), Pd (Z = 46), Ag (Z = 47), In (Z = 49) , and Sn (Z = 50) are measured at high temperature, mostly in the liqu id phase, to reduce the intensity of the structural extended x-ray abs orption fine structure (EXAFS) contribution. Main anomalies, showing a regular trend as a function of Z, are identified in the region around 100 eV and in the range 200-800 eV above an edge. They are assigned t o the opening of absorption channels creating double-hole configuratio ns such as [1s4p], [1s, 3d], and [1s3p]. Differences of self-consisten t calculations in the Dirac-Fock approximation have been performed and the dominant transitions unambiguously identified. The results are re levant for the improvement of the EXAFS analysis at these edges.