To date 268 even and 255 odd atomic energy levels in Th I have been found. The lowest level of the configuration 5f 6d 7s2 is 3H40 and lies 7795.27 cm-1 above the ground level 3F2 of 6d2 7s2, Some levels of 5f 6d2 7s and 6d2 7s 7p are identified.
ROMUALD ZALUBAS, "Present State of Analysis of the First Spectrum of Thorium (Th I)," J. Opt. Soc. Am. 58, 1195-1195 (1968)