Chapter 11 - Floppy Molecules

Abstract

An outline of the particular features in the spectra of molecules with more interconvertible geometries is given in this chapter. We discuss molecular inversion and inversion doubling in ammonia, and internal rotation. Level splitting caused by the hindered internal rotation in the spectra of molecules like acetaldehyde or methanol, and ethane-like molecules, is also discussed. Special attention is given to the effects of the coupling of the angular momenta generated by vibrational motion and internal rotation (torsional Coriolis coupling), and the interplay with the coupling of the internally rotating molecular moieties (hindering barrier and its dependence on molecular deformations). Typical limit-coupling states are defined by the methods of group theory.