Analysis of the third spectrum of dysprosium (Dy III )

The third spectrum of dysprosium has been observed in a sliding-spark discharge with a 10.7-m normal-incidence spectrograph in the wavelength region between 2007 and 5020 Å. Of the 2500 lines that were attributed to Dy iii, 544 are classified. With these data 106 energy levels were established, including five of the 5I ground term of the 4f10 configuration, 49 of 4f95d, 15 of 4f96s, and 37 of 4f96p. The levels have been interpreted theoretically and have been assigned percentage compositions in the most appropriate coupling schemes. Using semiempirical calculations with least-squares-fitted radial parameters, we have obtained average deviations between experimental and calculated levels of ±49,±29, and ±16 cm-1 for the 4f95d, the 4f96p, and the 4f96s configurations, respectively. The overlapping configurations 4f95d and 4f96s show slight evidence of configuration interaction. This analysis leaves Pm iii as the last spectrum of a doubly ionized rare earth to remain uninterpreted. With these data, a value of 184 970 ± 800 cm-1 has been derived for the ionization energy.