STRUCTURE OF SPECTRUM OF NEUTRAL TERBIUM TB-I .V. CONFIGURATION 4F85D26S

The even level system in Tb I which has been assigned to the electron configuration 4f85d6s2 in preceding papers has now been extended with a 10G term that marks the beginning of the configuration 4f85d26s. Its lowest levels follow a distorted pattern very much similar to that of the 8G ground term, notwithstanding the fact that the experimental g-factors are close to the Landé values. Comparison with other coupling schemes shows that the coupling in the new configuration is surprisingly near to the Russell-Saunders limit. Several of the strongest lines in the spectrum which do not show a trace of self-reversal are now classified as transitions to 10G 17 2, 15 2, 13 2, 11 2 while many other odd levels do not combine at all with the new levels. This opens the possibility of discriminating between the odd configurations 4f85d6s6p + 4f85d26p on the one hand and 4f86s26p on the other. Some new odd levels have been established thanks to their strong transitions to the new configuration. The even 10G is complete except for 10G 1 2 which is expected around 11000 K. The number of newly classified lines is 787 whereby the total number of classified Tb I lines is raised to 4020, being combinations between 36 even and 318 odd levels. © 1969.