@article{oai:nifs-repository.repo.nii.ac.jp:00011171,
 author = {KOIKE, Fumihiro and SUZUKI,  Chihiro and MURAKAMI,  Izumi and KATO,  Daiji and TAMURA,  Naoki and NAKAMURA,  Nobuyuki},
 issue = {3},
 journal = {Physical Review A},
 month = {Mar},
 note = {Extreme ultraviolet (EUV) optical transitions of lanthanide highly charged ions have been studied. The [Ni]4s24p–[Ni]4s24d and [Ni]4s24p–[Ni]4s4p2 transition lines of galliumlike lanthanide elements have been spectroscopically measured in large helical device (LHD) plasma and electron-beam ion trap (EBIT) plasma. The wavelengths for Eu ions agreed within 0.03% between the LHD and EBIT measurements. Due to the enhancement of spin-orbit interactions along with the increase of atomic number Z in 4p atomic orbitals, energy splitting between 4p1/2 and 4p3/2 orbitals increases significantly from lanthanum to lutetium, causing the crossing of Z-dependent wavelength curves. The spectral line positions and strengths are theoretically calculated by means of the multiconfiguration Dirac-Fock method. The mixing of the [Ni]4s24d and [Ni]4s4p2 configurations leads to an avoided crossing in the apparent wavelength curves. The configuration mixing makes both the [Ni]4s24p–[Ni]4s24d and [Ni]4s24p–[Ni]4s4p2 lines well visible in the EUV spectra near the level crossing point. The levels are found to cross between Z=62 and 63.},
 title = {Z-dependent crossing of excited-state energy levels in highly charged galliumlike lanthanide atomic ions},
 volume = {105},
 year = {2022}
}