Hyperfine structure and isotope shift measurements of unclassified lines in Eu II and new determination of the partition function

Abstract

Results of the measurements of isotope shifts and the hyperfine structure for 31 unclassified spectral lines of Eu II, obtained with the laser-induced fluorescence method, are presented. All experimental results are the first results available for these spectral lines. On the basis of measured hyperfine structure constants, J quantum numbers and fluorescence channels (by comparison to the theoretically predicted values), identification of electronic levels was accomplished. The lower levels of the lines investigated were identified as levels belonging to configuration 4f76s. On the basis of the literature values of isotope shifts for this configuration, isotope shifts for lower and upper levels were determined, and, with the use of a sharing rule, contributions of particular configurations in the spectroscopic description of these levels were evaluated. The number of configurations (cores) necessary for description of the Eu II spectrum and the resulting changes of partition function were estimated. Although, due to the lack of transitions to known electronic levels in Eu II, determination of absolute energies of the levels identified was impossible, probable energy values are presented, which might constitute a starting point for investigations in other spectral regions.