Discovery of new even-parity fine structure levels of Pr I with angular momenta 1/2, 3/2, and 5/2

Highlights: • Laser Induced Fluorescence Spectroscopy of Pr I atoms in Hollow Cathode Discharge Lamp. • Investigation of hyperfine structure constants of Pr I levels. • Discovery of 29 even parity fine structure levels of Pr I. • Classification of 130 spectral lines. The spectrum of Praseodymium was investigated in the visible region from 4000 Å to 7500 Å based on previously recorded Fourier Transform spectra. Source of free Pr atoms was a hollow cathode discharge lamp. The investigation of spectral lines was performed using laser-induced fluorescence spectroscopy. A tunable single mode ring-dye laser, pumped by a frequency doubled Nd-YAG laser, was used as the light source to investigate selected lines. Hyperfine spectra of 129 lines were recorded and the magnetic dipole hyperfine structure constants of the involved energy levels were determined. This led to the discovery of up to now unknown levels. In this paper, 30 even parity levels, having J-values of 1/2, 3/2, and 5/2 are presented. The existence of all levels is confirmed by several laser excitations in the spectral range of our dye laser.