A theoretical investigation of the fine structure of the 4$^2$P and 4$^2$D energy levels for the gallium isoelectronic sequence

The fine structure of the 4s$^2$4p$^2$P and 4s$^2$4d$^2$D energy levels for 50 ions of the gallium isoelectronic sequence has been investigated on the basis of previously calculated Dirac-Fock energies. There is smooth monotonous variation of the fine structure splitting along the isoelectronic sequence in the case of 4$^2$P levels, but in the case of 4$^2$D levels the same variation is rapid and irregular. It indicates that there is no substantial interaction of levels in the case of 4$^2$P levels and that the 4$^2$D levels are strongly perturbed. The allowance for 4s4p$^2$ configuration superposition leads, as a rule, to a satisfactory agreement between the theoretical and experimental results.