ABSTRACT
In this chapter, we concentrate exclusively on rigid molecules in isolated electronic states. For this important, but limited, class of molecules the vibronic states can be symmetry classified using the appropriate point group. We show here how the point group can be derived from the complete nuclear permutation inversion (CNPI) group by introducing the molecular symmetry (MS) group.
A rigid molecule is one for which there are no observable tunnelling splittings caused by wavefunction penetration between minima on the potential surface.
