The impact of dense plasma environments on the 1s3l fine structure levels of He-like ions

Finite-temperature dense plasma relativistic atomic structure calculations are employed to study the energy eigenvalues and transition probabilities related to the 1s3l fine structure levels of He-like ions. We discovered a particular response of the level structure that is distinctly different from simple nuclear charge screening effects that exists also for atoms and ions in vacuum as Z decreases. It is demonstrated that characteristic level crossings are driven by the free electron screening due to a particular dependence on the quantum numbers of each level of the 1s3l-configuration. Levels with large l shift stronger to the continuum than levels with small l whereas spin dependent dense plasma effects are relatively small. As a result, the known energy level fine structure in vacuum is subject to characteristic changes (level crossings, level order). Numerical calculations performed for a wide range of density, temperature and different chemical elements indicate that induced level crossings and change in level order are general characteristics of dense plasma effects.