Variation of the Observed Widths of La I Lines with the Energy of the Upper Excited Levels, Demonstrated on Previously Unknown Energy Levels

We performed systematic laser spectroscopic investigations of La I spectral lines, using optogalvanic detection. Sixteen previously unknown even parity levels, having energies between 40,300 and 44,300 cm−1, are reported. These levels classify altogether 67 lines, not listed in spectral tables. The new levels were found due to the Observation of the depopulation of the lower levels of the excited transitions. We found a remarkable variation of the observed widths of single hyperfine structure components dependent on the energy of the upper excited levels. Some levels having energies higher than 43,000 cm−1 appear to have a very high ionization probability.