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K-shell x-ray absorption by heavy atoms triggers multi-step decay processes via emission of x rays and Auger electrons as vacancies are transferred from core to valence shells.  This results in ranges of final charge states, e.g., 2⁺ to 8⁺ for Kr, due to different decay pathways [1]. When the core hole is produced in a heavy atom of a molecule, electrons from neighboring atoms participate in the decay cascade and result in ion fragmentation [1]. We are using high-resolution electron spectroscopy and coincidence ion-momentum spectroscopy to characterize core-hole decays.  Tunable x rays at the Advanced Photon Source excite K-shell electrons to pre-edge resonances and to the ionization continuum. Recent results include excitation and ionization of the Br K-shell of CF₃Br. The electron spectrometer provides photoelectron and Auger electron spectra that are complementary to ion-ion coincidence measurements. Understanding core-hole decays offers challenges to theory, including treatments of relativistic, electron correlation, and wave function relaxation effects [1] and molecular dynamics simulations of dissociative ionization processes [2].

[1] S. H. Southworth et al., Phys. Rev. A 100, 022507 (2019).

[2] A. E. A. Fouda et al., J. Phys. B 53, 244009 (2020).