The spectrum of protactinium has been photographed between 2500 Å and 9200 Å. The wavelengths of 8617 lines have been measured and the separation of the first and second spectra has been accomplished for 80% of the lines. Zeeman effects have been measured in the region between 4000 Å and 9000 Å. Thirty-two even levels and 252 odd levels have been found; these are listed together with their electronic angular momenta J and gJ values as derived from the Zeeman effect. The ground configuration of the neutral atom of protactinium is 5ƒ26d7s2.
A. GIACCHETTI, "First Spectrum of Protactinium," J. Opt. Soc. Am. 56, 653-656 (1966)