Whereas molecular symmetries usually are described by the Schonflies symbols, a set of labels devised by Mulliken is more frequently applied to atomic and molecular orbitals. These rely on identification of the same set of symmetry elements as is used for the Schonflies notation: a center of inversion, various rotational axes, Cn, and mirror planes, sv and sh.
| Mulliken Symbol | Interpretation |
|---|---|
| a | Non-degenerate orbital; symmetric to principal Cn |
| b | Non-degenerate orbital; unsymmetric to principal Cn |
| e | Doubly degenerate orbital |
| t | Triply degenerate orbital |
| (subscript) g | Symmetric with respect to center of inversion |
| (subscript) u | Unsymmetric with respect to center of inversion |
| (subscript) 1 | Symmetric with respect to C2 perp. to principal Cn |
| (subscript) 2 | Unsymmetric with respect to C2 perp. to principal Cn |
| (superscript) ' | Symmetric with respect to sh |
| (superscript) " | Unsymmetric with respect to sh |