Molecular Vibrations

Abstract

Vibration is a special kind of motion: the atoms of every molecule are constantly changing their relative positions at every temperature (even at absolute zero) without changing the position of the molecular center of mass. In terms of the molecular geometry, these vibrations amount to continuously changing bond lengths and bond angles. Symmetry considerations will be applied to the molecular vibrations in this chapter following primarily Refs. [5-1],[5-3]. Our brief discussion is only an indication of yet another important application of symmetry considerations. The mentioned references and two other fundamental monographs [5-4][5-5] on vibrational spectroscopy are suggested for further reading. Our primary concern will be to examine in simple terms the following question. What kind of information can be deduced about the internal motion of the molecule from the mere knowledge of its point-group symmetry?