Electric Octupole Transitions in Ag-like High-Z ions*

We report measurements and identifications of electric octupole (E3) transitions between the 4f_7/2,5/2 and 5s_1/2 levels of Ag-like W²⁷⁺, Re²⁸⁺, and Ir³⁰⁺ ions. We used a flat-field grazing-incidence extreme-ultraviolet (EUV) spectrometer on the electron beam ion trap (EBIT) of the National Institute of Standards and Technology (NIST) to record spectra that included lines from Ag-like and neighboring charge states. Our results confirm the occurrence of E3 transitions in W²⁷⁺, first reported by Sakaue et al. [1], and provide higher precision results for the wavelengths that our multi-configuration Dirac-Fock (GRASP2K) calculations can reproduce. 

Our collisional-radiative calculations based on the NOMAD [2] and FAC [3] codes give an insight into the population kinetics for Ag-like ions of heavy elements, including the electron density dependence of the relative line intensities. Our measurements of the forbidden lines in highly charged ions provide information on quantum-electrodynamic and relativistic effects of atomic structure and offer new diagnostic techniques for hot low electron density plasmas.

References

[1] H.A. Sakaue et al, Phys. Rev. 100, 052515 (2019)

[2] Yu. Ralchenko, Y. Maron, JQSRT 71, 609 (2001)

[3] M.F. Gu, Can. J. Phys. 86, 675 (2008)