Prominent role of multi-electron processes in K-shell double and triple photodetachment of oxygen anions

TL;DR

This study investigates multi-electron processes in K-shell double and triple photodetachment of oxygen anions using high-resolution experiments and ab-initio calculations, revealing the significant role of multi-electron interactions.

Contribution

The paper provides precise measurements and advanced calculations showing the importance of multi-electron effects in oxygen anion photodetachment, improving understanding of electron correlation effects.

Findings

High-resolution measurements of resonance positions and widths.

Good agreement between theory and experiment when including shake-up processes.

Confirmation of discrepancies in absolute cross sections between theory and experiment.

Abstract

The photon-ion merged-beams technique was used at a synchrotron light source for measuring absolute cross sections of double and triple photodetachment of O$^{-}$ ions. The experimental photon energy range of 524-543 eV comprised the threshold for K-shell ionization. Using resolving powers of up to 13,000, the position, strength and width of the below-threshold 1s 2s2 2p6 2S resonance as well as the positions of the 1s 2s2 2p5 3P and 1s 2s2 2p5 1P thresholds for K-shell ionization were determined with high precision. In addition, systematically enlarged multi-configuration Dirac-Fock calculations have been performed for the resonant detachment cross sections. Results from these ab-initio computations agree very well with the measurements for the widths and branching fractions for double and triple detachment, if double shake-up (and -down) of the valence electrons and the rearrangement of the electron density is taken into account. For the absolute cross sections, however, a previously found discrepancy between measurements and theory is confirmed.