Prediction and Measurement of Resonant and Nonresonant Shake Effects in the Core-level X-ray Emission Spectra of 3d^0 Transition Metal Compounds

Shake effects, which occur because of the sudden change in core potential due to photoexcitation, are well known in x-ray photoelectron spectroscopy (XPS) and closely related methods, and regularly lead to satellite peaks due to many-body excitations. It has been thought, however, that shake effects have little effect on core-to-core x-ray emission spectroscopy (CTC-XES), where the difference in core hole potentials upon radiative decay are rather small. Here we demonstrate that shake effects are prominent specifically in the Kα XES from 3d transition metal systems with nominally zero valence electrons, i.e., 3d^0 systems. First, we demonstrate that valence level shake satellites are amplified via interference due to a resonance between the 2p3/2-hole (Kα1) plus valence level shake state, and the 2p1/2-hole (Kα2) state. Second, the shake satellite from the Kα2 transition is indeed predicted to be weak, but is experimentally observed here, providing further independent verification of our model. The prediction includes a detailed analysis of 2p to 1s Kα XES using density functional theory (DFT)-augmented multiplet ligand field theory (MLFT). This work presents a rich interpretation of CTC-XES in the context of shake excitations and highlights its potential as a probe of valence level dynamics.