Derivation of states arising from configurations

In the case of atoms, deriving states from configurations, in the Russell-Saunders approximation (Section 7.1.2.3), simply involved juggling with the available quantum numbers. In diatomic molecules we have seen already that some symmetry properties must be included, in addition to the available quantum numbers, in a discussion of selection rules. 

In deriving states from orbital configurations, symmetry arguments are even more essential. However, those readers who do not require to be able to do this may proceed to Section 7.2.5. 

The symmetry species of the orbital part of the electronic wave fimction 

Note that a cr MO is not usually labelled cr+, which it should really be, as there are no a  

2 ELECTRONIC SPECTROSCOPY OF DIATOMIC MOLECULES The ground configuration of oxygen is 

8 The labelling of the B3 II0+ state follows general usage rather than convention, which would label it b3l7of. 

The symmetry species T(ij/°) of the orbital part of the electronic wave function corresponding to a particular configuration is given by 

9 Upper-case Greek letters are used for states, lower-case letters are used for orbitals. 

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