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Spectrum and Term System of Be III

The spectrum of helium-like beryllium, Be III, has been recorded in the wavelength region 500-6 200 Å. By means of the new measurements and some previous ones the term system has been recalculated. The ionization energy of 1s2 1S has been determined to 1 241 242 ± 15 cm-1. Comparisons are made with theoretical calculations of ionization energies. The Lamb shifts in 2s 1S and 3S are determined to -2.8 cm-1 and -4.2 cm-1, respectively. Ritz formulae and other semi-empirical relations are established, permitting an unlimited extension of the term system.