Theory of molecular spectra

After reviewing the spectroscopic properties of diatomic molecules and the main types of coupling, a detailed study of the spectra of diatomic molecules is presented according to the nature of the transitions: rotational, vibrational or electronic.

Due to the complexity of vibrations and rotations in polyatomic molecules, only a few generalities are given on the rotational spectra and molecular vibrations associated with these molecules.

Molecules can emit radiation after being excited by an incident electromagnetic wave. If the incident radiation is absorbed during the process, the re-emitted light is said to fluoresce; on the other hand, when there is no absorption of the exciting radiation, the phenomenon is called scattering. Both aspects are discussed at the end of this article.

For further information, readers may refer to the general works to given in the bibliographic references, as well as to recent publications .

The study of atomic spectra was the subject of the article in this volume (reference ).