SPECTRUM AND ENERGY-LEVELS OF 5-TIMES-IONIZED NIOBIUM (NB VI)

The spectrum of the kryptonlike ion Nb VI was observed from 325 to 270 0 angstrom with sliding-spark discharges on 10.7-m normal-incidence an d grazing-incidence spectrographs. Experimental energies were determin ed for all levels of the 4s(2)4p6, 4s(2)4p(5)4d, 4f, 5s, 5p, 5d, 5g, 6 s, and 4s4p(6)4d configurations as well as for some levels of the 4s(2 )4p(5)6g and 6h configurations. A total of 303 lines are now classifie d as transitions between 99 observed levels. Large hyperfine splitting s were found for several levels of the 4p(5)5s and 5p configurations. The observed configurations were theoretically interpreted by means of Hartree-Fock calculations and least-squares fits of the energy parame ters to the observed levels. An improved value of the ionization energ y was determined from the 4p(5)5g, 6g, and 6h configurations. The adop ted value of the limit is 823 240 +/- 50 cm-1 (102.069 +/- 0.006 eV).