Qualitative intramolecular quantum dynamics

The state-of-the-art symmetry methods for the consistent quantum-mechanical treatment of intramolecular motions are reviewed. It is shown that for a broad class of topical problems, these methods are not only self-sufficient but, at present, the only possible ones. In particular, they greatly simplify the analysis of nonrigid molecules, for which conventional, analytical equation-of-motion methods run into serious mathematical difficulties even at low excitation energies.