Threshold excitation in Fe Kα3,4 satellites

Fe Kα3,4 satellite spectra are investigated using a Johann-type spectrometer at the BL15XU undulator beam line, SPring-8. The intensity of the Kα3,4 satellite relative to the Kα1 emission line is found to increase asymptotically with excitation energy up to 9000 eV, almost saturating at 10 000 eV. The satellite threshold energy is found to be 7882 ± 14 eV. This corresponds to the ionization energy of Fe 1s + 2p*, where * indicates that the value is from the Z + 1 approximation. The appearance of a small peak around the [1s2s] double ionization energy suggests that the satellite intensity with the excitation energy can be increased not only by the formation of the 2p spectator holes, but also by a combination of the [1s2s] resonance and [2s2p] Coster-Kronig transition