A study of Mg IV between 80 and 2100 Å has led to the classification of 243 lines. A total of 23 odd and 64 even levels have been identified as belonging to the 2s2p5, 2s2p6 , 2s2p53s, 2s22p43p, 2s22p4ns, and 2s22p4nd (n = 3, 4, 5) configurations. Matrix diagonalizations and least-squares fits to the observed levels lead to well-defined radial integrals and verify the level assignments. On the basis of comparisons in the F I isoelectronic sequence, designation changes are suggested for some 2p4(3P)3d levels of Na III, Al V, Si VI, P VII, and S VIII. New levels are given for Na III and Al V, and some previously listed levels in Na III and S VIII are rejected as unreal. An ionization energy of 880 800 cm-1 is given for Mg VI.
MARIE-CHRISTINE ARTRU and VICTOR KAUFMAN, "Analysis of the Spectrum of Triply Ionized Magnesium (Mg IV)," J. Opt. Soc. Am. 62, 949-957 (1972)