Group theoretical aspects of band intensities in octahedral complexes

Group theoretical aspects of band intensities in octahedral complexes 

The most general selection rule for electric-dipole transitions, the type of transition that is relevant to almost all of the bands observed in the electronic spectra of transition metal complexes, is a group theoretical statement of the excitation process described in qualitative terms in Section 8.1. It is the following  

An electronic transition is electric-dipole allowed if the direct product of the symmetries of the ground and excited electronic terms of a molecule contains the symmetry species of one or more coordinate axes, both ground and excited terms having the same spin multiplicity. 

This selection rule sounds somewhat formidable but in practice it is not difficult either to understand or apply. The coordinate axes come in because 

This table is actually the product table for the 0 point group for the point group Of, the usual suffix rule applies gxg = uxu=g gxu = u. 

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