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 features at the K edges of fifth-period elements is reported. Samples of MoCx (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 liquid phase, to reduce the intensity of the structural extended x-ray absorption 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 to the opening of absorption channels creating double-hole configurations such as [1s4p], [1s, 3d], and [1s3p]. Differences of self-consistent calculations in the Dirac-Fock approximation have been performed and the dominant transitions unambiguously identified. The results are relevant for the improvement of the EXAFS analysis at these edges.