X-ray line shifts and delocalization of levels of He-like ions are studied within the framework of the self-consistent multi-configuration relativistic finite temperature ion sphere model. A set of analytical equations for an N-electron bound atomic system to determine X-ray line shifts and level delocalization is proposed that provides very good agreement with numerical calculations, newly high precision line shift measurements of the 1s3pP11−1s2S01Heβ transition in Cl15+ and the 1s3pP11-level delocalization in Al11+. We re-analyzed the recently claimed discrepancy between the predictions from the ion sphere model, analytical approaches and the data. The analytical b-potential approach that imitates lattice effects via a perturbation of the free electron distribution in the in sphere is developed and contrasted with currently unexplained line shift measurements of the 1s2pP11−1s2S01Heα transition in Al11+.
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