*Article* **Satellite Excitations and Final State Interactions in Atomic Photoionization**

**Victor G. Yarzhemsky 1,\* and Yury A. Teterin 2,3**


**Abstract:** Satellite excitations and final state configuration interactions appear due to the manyelectron correlations and result in a photoelectron spectrum complex final state structure instead of single lines corresponding to one-hole states. In the present work, both processes are considered in a framework of the many-body perturbation theory, and two techniques, namely the spectral function and CI (configuration interaction) methods are considered. It is shown that for the calculation of satellite lineshapes and low-energy Auger decay, the spectral function method is more appropriate, but in the case of strong final state interactions, the methods of solution of Dyson equation or secular matrix are superior. The results obtained for satellites and low energy Auger decay in the Ne 1s, Ne 2p photoelectron spectra, the Co 3s, and the Th 5p photoelectron spectra are in agreemen<sup>t</sup> with the experimental data.

**Keywords:** atomic photoionization; photoelectron spectroscopy; many-electron effects; satellites; Ne 1s; Ne 2p; Co 3s; Th 5p photoelectron spectra

**Citation:** Yarzhemsky, V.G.;

Teterin, Y.A. Satellite Excitations and Final State Interactions in Atomic Photoionization. *Atoms* **2022**, *10*, 73. https://doi.org/10.3390/ atoms10030073

Academic Editors: Anatoli Kheifets, Gleb Gribakin and Vadim Ivanov

Received: 5 May 2022 Accepted: 5 July 2022 Published: 14 July 2022

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