Breakdown of the Independent Particle Approximation in High-Energy Photoionization

Abstract

The independent particle approximation is shown to break down for the photoionization of both inner and outer $n\ensuremath{\ell}$ $(\ensuremath{\ell}>0)$ electrons of all atoms, at high enough energy, owing to interchannel interactions with the nearby $\mathrm{ns}$ photoionization channels. The effect is illustrated for Ne $2p$ in the 1 keV photon energy range through a comparison of theory and experiment. The implications for x-ray photoelectron spectroscopy of molecules and condensed matter are discussed.