The influence of plasma screening on the 2s 2 1 S 0 → 2s2p 3 P 1 o intercombination and the 2s 2 1 S 0 → 2s2p 1 P 1 o allowed transitions is investigated theoretically for several ions along the Be I isoelectronic sequence ͑C III, N IV, O V, Si XI, Fe XXIII, and Mo XXXIX͒. For the case of a weakly coupled hot plasma, multiconfiguration Dirac-Fock computations have been carried out for these ions by considering a ͑time averaged͒ Debye-Hückel potential for both the "electron-nucleus" and

more »

... -electron" interaction. The plasma screening is found to enlarge the 2s 2 1 S 0 → 2s2p 3 P 1 o excitation energy uniformly along the Be I isoelectronic sequence, leading to an increasing blueshift of this intercombination line as the nuclear charge is increased. For the 2s 2 1 S 0 → 2s2p 1 P 1 o resonance line, in contrast, the transition energy is either blueshifted or redshifted in dependence of the screening parameter and owing to a cancellation of the plasma screening on the electron-nucleus and electron-electron interaction. This interplay of the ͑external͒ plasma screening with the internal interactions in the berylliumlike ions leads, for instance, to a shift of the resonance transition from red to blue in going from O V to Si XI ions. Apart from the screening effects on the transition energies, we also investigate their influence on the oscillator strengths and emission rates along the Be I isoelectronic sequence.