First Spectrum of Protactinium*

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 5f26d7s2.