Effect of nearest-neighbor ions on excited ionic states, emission spectra, and line profiles in hot and dense plasmas

A two-center model is used to study the influence of the cylindrical symmetry, imposed by the nearest neighbor, on the ionic levels and emission spectra of a Li-like krypton ion immersed in hot and dense plasma. The symmetry breaking of the spherical symmetry of the local microfield in the peripheries of the ion due to the effect of its nearest neighbor is accounted for by expanding the total electric microfield into its multipole components. The resulting cylindrically symmetric Hamiltonian is diagonalized to obtain the energy levels in this distorted microfield. It is shown that the cylindrical symmetry mixes states with different l's (l is the orbital quantum number), particularly for highly excited states, and thereby gives rise to forbidden transitions in the emission spectrum. Results are obtained for (i) the variation of the ionic level shifts and mixing coefficients with the distance to the nearest neighbor and (ii) representative computed spectra to show the density effects on the spectral line profiles, shifts, and widths, and the forbidden components in the spectrum. It is found that by an ion density of 3×{}10²² cm^-3 forbidden lines can be of the same magnitude as the original allowed lines. Linewidths resulting from the distribution of nearest-neighbor distances are narrower than the result from the mechanism of Woltz and Hooper [Phys. Rev. A 38, 4766 (1988)]. Mixing is not important for the dominant ground-state configuration species of the plasma but rather enters through its major effects on excited-state properties.