The different possible vibracionals states of a molecule translate into a set of levels of energy. The separation among these levels of energy falls in the infrared region of the electromagnetic spectre. For obtaining the spectre from IR, she makes itself interoperate the ray of light infrared with the sample, and the amount of energy absorbed at each length of wave is registered.

With the exception of the enantiòmers, there are not two molecules that have the same spectre of IR. We can distinguish two zones to the spectre from IR according to the vibrations that are observed there:
 

• Between 4000 and 1300 cm^-1: a series of bands of absorption provoked are usually observed for simple vibrations of tension, that is between two atoms of the molecule. They identify to functional groups.
• Between 1400 and 600 cm^-1: bands of absorption of molecular vibrations, the assignment of which is more difficult, are usually observed since each of them is generated by individual absorptions added up (complex vibrations). On the other hand, in this zone, the small differences in the structure of the molecule cause important variations in the maximums of absorption. Therefore, they are characteristics of a determinate compound and it is because of that that this zone of the spectre receives the name ofdigital impression.

THE'FT-IR it is one of the more versatile espectroscòpiques techniques and of major application in the characterisation and identification of materials (polymers, plastics, inorganic solids), analysis of pharmaceutical products and of synthesis, analysis of pollutants, forensic science, biomedicine, agriculture and feeding among others.

• Pamphlet of the Bruker Alpha FT-IR Spectrometer
• Specifications for the Bruker Alpha FT-IR Spectrometer