SPECTRUM OF DOUBLY IONIZED NIOBIUM (NB-III)

The spectrum of doubly ionized Nb is recorded in the region 900-2512 A ngstrom with the aid of a 6.65-m vacuum ultraviolet normal incidence s pectrograph. The (4d(2)5s + 4d5s(2))-4d5s5p and 4d(2)5p(4d(2)5d + 4d(2 )6s) transitions are identified and energy levels of the 4d5s(2), 4d(2 )5d, 4d(2)6s and 4d5s5p configurations are established. The wavelength s of previously investigated transitions 4d(3)-4d(2)5p and 4d(2)5s-4d( 2)5p are improved and their analysis is extended. The list of identifi ed Nb III transitions now contains 908 lines. All levels are now known in the 4d(3), 4d(2)5p, 4d(2)5s and 4d5s5p configurations except the 4 d(2)5s(S-1)S-2 level. 72 out of possible 83 levels of the interacting (4d(2)6s + 4d(2)5d) configurations are located.