PCI effects in argon 2p double Auger decay probed by multielectron coincidence methods

Electron correlations in three electron emission associated with inner shell photoionization are investigated for the first time through a combined theoretical and experimental approach. Namely, different kinds of post-collisional interactions (PCI) occurring in the decay of argon 2p holes by emission of two Auger electrons are isolated experimentally with a powerful coincidence technique and are modelled with an eikonal approach. It is shown that PCI distortion of the photoelectron line shape is stronger than in the single Auger paths and depends critically on the process: in direct double Auger decays where two Auger electrons are emitted simultaneously, direct interaction of the 2p photoelectron with the two Auger electrons is demonstrated; in cascade double Auger processes, the PCI distortion depends only slightly on the last electron emitted in the cascade. This perturbation depends on and reveals the lifetime of the intermediate Ar^{2 +} state.