The positions of 38 observed levels of the 4ƒ3 configuration of Pr III were calculated with a rms error of ±168 cm−1, by use of seven adjustable parameters, The interaction with the 4ƒ5d2 levels is discussed. A calculation of the levels of the 4ƒ25d configuration was obtained with a rms error of ±182 cm-1 relative to the 101 observed levels, utilizing 13 adjustable parameters.
RICHARD E. TREES, "4ƒ3 and 4ƒ25d Configurations of Doubly Ionized Praseodymium (Pr III)," J. Opt. Soc. Am. 54, 651-657 (1964)