Irreducible representations fourfold degenerate

Finally, the fourfold degenerate irreducible representation components may be written as ... 

In this table, there exist four non-degenerate Irreducible representations, one twofold degenerate and four fourfold degenerate. From this table and that of acetone with the cog-wheel effect, the equivalence relations between the irreducible representations of both groups are derivable. These are given in Table 13. 

The rules for labeling these irreducible representations are summarized in Table 6.5. The labels 2, II, A, and so on are used only for the linear molecule groups Ccov and D h- For the nonlinear molecules, A and B states are nondegenerate (with A states symmetric with respect to rotation about the principal axis), E states are doubly degenerate, T or F states are triply degenerate, and G states are fourfold degenerate. Subscripts and superscripts then provide keys for other symmetry elements (if any), and the u or g subscript always appears if inversion is a member of the group. 

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