Double resonance, fluorescence spectroscopy, and hyperfine structure in Pr I

Laser-fluorescence spectroscopy and the laser-rf double-resonance method are combined to classify lines in the Pr I absorption spectrum. The double-resonance technique is found to be particularly valuable for this purpose since, by focusing on the lower level of a transition, it leads in many cases to unique line assignments. Precise (∼ 1 ppm) measurements are reported for the hyperfine-structure (hfs) constants of 15 low levels, and 0.5% values for 34 higher levels. Classifications are given for many lines in the region $5746<\mathrm{}\lambda <6148\mathrm{}$ Å. Preliminary values are derived from the double-resonance data for the single-electron hfs integrals $a_{4f}$, $a_{5d}$, $a_{6s}$, $b_{4f}$, and $b_{5d}$ for the low-electron configurations of Pr I.