Finding of previously unknown energy levels using Fourier-transform and laser spectroscopy

In this paper several possibilities of how to find previously unknown energy levels from high-resolution Fourier-transform or laser-generated spectra are discussed. As examples we use levels of neutral Ta, Pr and La. The following methods are used: analysis of Fourier-transform emission spectra, laser-excitation of unclassified spectral lines, analysis of the hyperfine structure of unclassified lines. The discovery of two new La I energy levels is reported.