Population trapping: The mechanism for the lost resonance lines in Pm-like ions

We report a population kinetics study on line emissions of the Pm-like Bi22+ performed by using a collisional-radiative (CR) model. Population rates of excited levels are analyzed to explain the population trapping in the 4f135s2 state which causes the loss of the 5s − 5p resonance lines in emission spectra. Based on the present analysis, we elucidate why the population trapping is not facilitated for a meta-stable excited level of the Sm-like Bi21+. The emission line spectra are calculated for the Pm-like isoelectronic sequence from Au18+ through W13+ and compared with experimental measurements by electron-beam-ion-traps (EBITs). Structures of the spectra are similar for all of the cases except for calculated W13+ spectra. The calculated spectra are hardly reconciled with the measured W13+ spectrum using the compact electron-beam-ion-trap (CoBIT) [Phys. Rev. A 92 (2015) 022510].