We report the recording of new highly resolved Fourier transform spectra of the neutral praseodymium atom. With the help of the new spectra we found about 9000 new lines, from which -in the region 3260 to 9880Å -1194 could be classified as transitions between energy levels of the Pr atom and 19 as transitions of the Pr ion. 23 new atomic energy levels of odd parity and one of even parity were discovered during this first examination. The spectra might be very helpful for further laser spectroscopic investigations of the hyperfine structure of Pr I and Pr II transitions.Confidential: not for distribution.

The hyperfine structure of weak La I lines was experimentally investigated using laser optogalvanic spectroscopy in a hollow cathode discharge lamp. More than 100 La I lines were investigated and 40 new energy levels were discovered, most of them having even parity. The magnetic hyperfine interaction constants A and in some cases the electric quadrupole interaction constants B for these levels were determined. All the newly discovered levels were confirmed either by additional laser excitations (from other known levels) or by lines in a Fourier transform spectrum which could now be classified.

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.

We report the discovery of about 140 new energy levels of the neutral praseodymium atom, found by means of laser-induced fluorescence spectroscopy. Their energy has been determined with an uncertainty of 0.010 cm−1 using a wave number calibrated Fourier-transform spectrum.

Laser excitation of an Ar–La plasma, generated in a hollow cathode discharge lamp, has allowed to us observe a huge number of spectral lines that could not be interpreted as transitions between already known La energy levels. From the observed hyperfine structure patterns and fluorescence lines, we derived 37 new La levels, all with even parity, in the energy range between 38 000 cm−1 and 43 000 cm−1. The existence of these levels was then proved by excitations from other known lower levels.