Notation doubly degenerate orbital

The notation n that is used here is almost never strictly correct according to group theory, where it reserved for doubly degenerate orbitals in linear molecules (Chapter 6). It is, however, widely used to refer to loal symmetry the expression n interaction is used when the two orbitals share a common nodal plane and have lateral overlap (3-1). 

Labels refer to the notation of A-orbitals and (A, S)-terms appropriate for linear symmetry (Doon)- This has the same consequencies for d-orbitals as the trigonal symmetry D31,. 2 is orbitally non-degenerate and 77 and A are doubly degenerate. This is also true for if formed from d-electrons, whereas it could split in the general case of Dsh. 

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