Extended Analysis of the Spectrum of Mg III

The spectrum of Mg III has been thoroughly investigated in the wavelength range 720 to 6 600 Å by using powerful spectrographs. The earlier analysis has been checked and slightly revised. The analysis has been greatly extended to configurations with higher n and l values and the following configurations are now complete: 2 p 5 3 s , 4 s , 5 s , 3 p , 4 p , 3 d , 4 d , 4 f , 5 f , and 5 g . Accurate level values have been derived. The number of identified lines is 373. The ionization energies have been derived by applying the polarization formula to 4 f , 5 f and 5 g giving for 2 p 52 P 1½ 646 402±5 cm -1 . The 2 p 5 3 s , 3 p , and 3 d configurations are best described in the LS coupling scheme, and 4 s , 5 s , 4 p , 4 f , 5 f , and 5 g in the J K scheme.