91 Pa :   5f2(3H4) 6d 7s2 92 U :   5f3(4Io9/2) 6d 7s2 93 Np :   5f4(5I4) 6d 7s2 103 Lr :   5f14 7s2 7p1 question-marked 104 Rf :   5f14 6d2 7s2 question-marked CRC David R. Lide (ed), CRC Handbook of Chemistry and Physics, 84th Edition, online version.