Laser induced fluorescence and optogalvanic spectroscopy applied to find previously unknown energy levels of La I and studies of their Zeeman structure

•14 new high-lying even parity energy levels of La I were discovered.•We identified and classified 46 previously unassigned very weak La I lines.•New method of Lande gJ factors measurement was used for observation of weak La I lines.•By the use of optogalvanic technique precise spectroscopic data have been obtained; new experimental gJ factors have been determined for 5 energy levels of La I.•Hfs data for previously known La I levels have been tested and corrected.

After the excitation of the La-Ar plasma in a hollow cathode lamp we observed in optogalvanic spectra a number of atomic lines that could not be interpreted as transitions between already known La energy levels. Using the laser induced fluorescence (LIF) method and computer simulations of the hyperfine structure patterns, we derived 14 unknown La levels, all with even parity, in the energy range between 40 877  cm−1 and 43 485  cm−1. The existence of these levels was then confirmed by excitations from other known lower levels. We performed also investigations of the Zeeman structure of some of these lines in order to verify the J values of newly found levels and to determine their gJ factors.