Time-Resolved X-Ray Spectroscopy from the Atomic Orbital Ground State Up

X-ray spectroscopy has been a key method to determine ground- and excited-state properties of quantum materials with atomic specificity. Now, new x-ray facilities are opening the door to the study of pump-probe x-ray spectroscopy—specifically, time-resolved x-ray absorption (trXAS) and time-resolved resonant inelastic x-ray scattering (trRIXS). In this paper, we will present simulations of each of these spectroscopies using a time-domain full atomic multiplet, charge-transfer Hamiltonian adapted to study the properties of a generalized cluster model including a central transition-metal ion caged by ligand atoms in a planar geometry. The numerically evaluated trXAS and trRIXS cross sections for representative electron configurations 3d9 and 3d8 demonstrate the insights that can be obtained from charge-transfer pumping and how this nonequilibrium process affects ground- and excited-state properties. The straightforward characterization of the excitations in these systems based on our analysis of the simulations can serve as a benchmark for future experiments, as access to these time-resolved spectroscopic techniques becomes more widely available. Published by the American Physical Society 2025