The spectrum of Pr3+ produced by a sliding spark discharge was photographed in the wavelength range of 800 to 3100 Å with a 35-ft Eagle vacuum spectrograph. An analysis of the resulting line list led to the discovery of all the levels of the 4ƒ2 (except the 1S0), 4ƒ5d, 4ƒ6s, and 4ƒ6p configurations. The interaction parameters for each configuration were derived from a least-squares fit of the energy formulas to the observed levels.
JACK SUGAR, "Analysis of the Spectrum of Triply Ionized Praseodymium (Pr IV)," J. Opt. Soc. Am. 55, 1058-1059 (1965)