New energy levels and hyperfine structure measurements of neutral lanthanum by laser-induced fluorescence spectroscopy

This study is focused on the search for new energy levels and the classification of weak spectral lines by analysing hyperfine (hf) spectra. Laser-induced fluorescence spectroscopy as well as optogalvanic spectroscopy were applied to measure the hf structure of Lanthanum transitions. Free La atoms are produced and excited in a hollow-cathode discharge. Ninety-six spectral lines have been analysed in the spectral range from 430 to 742 nm using a tunable single-mode cw dye laser operating with different dyes. Ninety-four of these lines are new, which means they are not listed in commonly used wavelength tables. A classification program was used to classify these 94 lines. Eighteen new energy levels were discovered. They were confirmed by further laser excitation. Fifty-one other spectral lines were classified via their hf pattern and centre-of-gravity wavenumber from Fourier transform spectra in order to prove the new even energy levels. In addition, 31 spectral lines were observed and classified as fluorescence transitions from the excited upper levels. A total of 176 spectral lines could be classified in this work. Seventy-three magnetic dipole hf structure constants A for the upper energy levels of the transitions were determined and compared with references, if available. Twenty-three of these constants are measured for the first time (including the A constants for 18 new levels)