Influence of dense plasma on the low-lying transitions in Be-like ions: relativistic multiconfiguration Dirac–Fock calculation

The ion-sphere model for a strongly coupled dense plasma is applied to investigate the influence of plasma screening on the low-lying 2s 2 1 S 0 → 2s2p 1 P 1 o resonance and 2s 2 1 S 0 → 2s2p 3 P 1 o intercombination transitions of beryllium-like ions. Detailed computations have been performed for the ions O 4+ , Ne 6+ , Si 10+ , Ar 14+ , Fe 22+ and Mo 38+ , based on multiconfiguration Dirac–Fock wavefunctions. The plasma screening is found to increase the excitation energy along the whole isoelectronic sequence, leading to a quite sizeable blueshift of these lines. For a given plasma density, the blueshift for the 1 S 0 → 3 P 1 o intercombination line is usually larger than that for the 1 S 0 → 1 P 1 o resonance line. For a given ion, moreover, the shift increases as the plasma density is enlarged, i.e. for a more and more strongly coupled plasma. In particular, the intensity ratio of the resonance-to-intercombination line appears sensitive with regard to the electron density in the plasma. The effect of a strongly coupled dense plasma on the oscillator strengths and emission rates is also reported.