Relativistic effects in hydrogenlike atoms embedded in Debye plasmas

Dynamic polarizability of an atomic ion within a dense plasma

We analyze the influence of plasma electron density on frequency-dependent linear field-response behavior of an atomic ion embedded in a dense plasma medium. The frequency-dependent atomic response, characterized by the dynamic dipole polarizability α(d)(ω) as a function of the angular frequency ω of the time-dependent field, is estimated here up to the first pole of α(d)(ω) on the ω axis (corresponding to the lowest resonance transition 1s(2 1)S→1s2p(1)P) for the ground state 1s(2 1)S of a two-electron atomic ion Ne(8+) (Z = 10) at different plasma electron densities, as a typical example, employing the time-dependent coupled Hartree-Fock scheme within the framework of the ion-sphere model. It is observed that, owing to plasma density-induced enhancement of α(d)(ω) at every ω, the pole position of α(d)(ω) on the ω axis retracts toward the origin. This indicates a density-induced lowering (redshift) of the corresponding transition energy that conforms to experimentally observed trends. The polarizability calculation suggests a density-induced drop in the 1s(2 1)S→1s2p(1)P absorption oscillator strength in the atomic ion within dense plasmas.

Photodetachment of H- in dense quantum plasmas

We have made an investigation to study the plasma screening effect of dense quantum plasmas on the photodetachment cross section of hydrogen negative ion within the framework of dipole approximation. Plasma screening effect has been taken care of by the exponential cosine-screened Coulomb potential (ECSCP). The asymptotic forms of highly correlated wave functions for the initial bound states of H(-) and the plane wave form for the final e(-)-H states are used to evaluate the transition matrix elements. Results for photodetachment cross section in dense quantum plasmas are reported for the plasma screening parameter in the range [0.0,0.6] (in a(0)(-1)). In respect of the photodetachment process of H(-), we have also compared the plasma screening effect of a dense quantum plasma with that of a weakly coupled plasma for which plasma screening effect has been represented by the Debye model. Our results for the unscreened case agree nicely with some of the most accurate results available in the literature.

Be I isoelectronic ions embedded in hot plasma

The influence of plasma screening on the 2s(2 1)S0-->2s2p(3)p(0)1 intercombination and the 2s(2 1)S0-->2s2p(1)p(0)1 allowed transitions is investigated theoretically for several ions along the isoelectronic sequence (C III, N IV, O V, Si XI, Fe XXIII, and Mo XXXIX). For the case of a weakly coupled hot plasma, multiconfiguration Dirac-Fock computations have been carried out for these ions by considering a (time averaged) Debye-Hückel potential for both the "electron-nucleus" and "electron-electron" interaction. The plasma screening is found to enlarge the 2s(2 1)S0-->2s2p(3)p(0)1 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)S0-->2s2p(1)p(0)1 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 (external) 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.