ABSTRACT
Infrared spectroscopy is one of the most used spectral methods in organic analysis, in particular in functional analysis. This chapter is essentially devoted to some aspects of the theory of infrared spectra. It is studied successively as the spectra of rotation pure and vibration-rotation of diatomic molecules. The case of polyatomic molecules is equally evoked. Firstly, the domains of infrared spectroscopy are specified. They correspond to levels of rotational, vibrational, and rotational-vibrational energies of a diatomic molecule. Then, are also specified the different motions which animate the molecules. A non-linear molecule constituted by n atoms can be animated by three motions, translation, rotation and of vibration of the atoms. Mathematical relations concerning the levels of energy of pure rotation and those of energy of pure vibration and another giving the energy of vibration rotation exist. Their establishment is given in the chapter. They are obtained by starting from models somewhat simplified.
