Electron Impact Excitation of Ge-like Te20+–Cd16+ Ions

Abstract

We study electron impact excitation of dipole allowed transitions in the extreme ultraviolet range—8–55 nm—for the germanium isoelectronic sequence Te20+–Cd16+. The fine structure transitions between the ground state having configuration 4s24p2 and the excited states with configurations 4s4p3 and 4s24p4d are considered for these ions. We employ the relativistic distorted wave method to calculate the excitation cross sections in the incident electron energy range from the excitation threshold to 5000 eV. To obtain the required ionic bound state wavefunctions we have used the multi-configuration Dirac-Fock method with correlations within the n = 5 complexes as well as performed relativistic configuration interaction calculations to include the quantum electrodynamic effects. The accuracy of these wavefunctions is established by comparing our calculated wavelengths and oscillator strengths of the considered transitions with the previously reported measurements and other available theoretical results. We also provide the fitting parameters of the calculated cross sections and the excitation rate coefficients for their direct applications in plasma modeling.

Collision Strengths of Astrophysical Interest for Multiply Charged Ions

“…Collision strengths have been calculated (and tabulated) for a number of light, medium, and heavy ions, cf. [52,53] and-more recently-also for fine-structure-resolved, low-lying excitations of ions with a complex shell structure, such as germanium-like [54] or even Co 2+ ions with an open 3d shell [55]. Despite the need for such data for radiation transfer or non-LTE simulations, the good number of notations for specifying the energies, shell coupling, and quantum numbers of the ionic levels involved, as well as different averaging procedures have surely hampered the use and comparison of collision strengths in the literature.…”