The Spectrum of O III

The spectrum of two times ionized oxygen, O III, has been observed with a theta-pinch discharge as a light source. About 750 lines have been measured in the wavelength region 500-8500 A; about 450 of these are new lines. By using only lines above 500 A the whole energy-level system has been recalculated. On the basis of the new measurements, calculated wavelengths are given for 147 lines in the region 228-500 A, suitable as reference lines. By applying the polarization formula to the hydrogen-like levels, the ionization limit has been determined to 443 084.7 ± 2 cm -1 .