Prediction and\nMeasurement of Resonant and Nonresonant\nShake Effects in the Core-Level X‑ray Emission Spectra of 3d<sup>0</sup> Transition Metal Compounds

Shake effects, resulting from sudden core potential changes\nduring\nphotoexcitation, are well-known in X-ray photoelectron spectroscopy\n(XPS) and often produce satellite peaks due to many-body excitations.\nIt has been thought, however, that they are negligible in core-to-core\nX-ray emission spectroscopy (CTC-XES), where the difference in core–hole\npotentials upon radiative decay is rather small. We demonstrate that\nshake effects are significant in Kα XES from 3d transition metal\nsystems with nominally zero valence electrons. We show that valence\nlevel shake satellites are amplified via interference due to a resonance\nbetween the 2p<sub>3/2</sub>-hole (Kα<sub>1</sub>) plus valence\nlevel shake state and the 2p<sub>1/2</sub>-hole (Kα<sub>2</sub>) state. Additionally, while the Kα<sub>2</sub> shake satellite\nis indeed predicted to be weak, we observe it experimentally, providing\nfurther independent verification of our model. This prediction includes\na detailed analysis of 2p to 1s Kα XES using density functional\ntheory (DFT)-augmented multiplet ligand field theory (MLFT).