According to McGraw-Hill Higher Education, the basics of Infrared (IR) spectroscopy correspond to interaction between radiation from the IR region within the EM spectrum. Within the molecule, excitation of the vibrations of polar covalent bonds, including bending and stretching modes, are caused by IR radiation.
As the IR region of the EM spectrum is scanned, the energy absorptions, such as the IR spectrum of butanal, are shown. Generally, an IR spectrum is divided into two approximate regions: the fingerprint region and the functional group region, which supplies most of the information needed to interpret an IR spectrum. The most important information regarding an IR spectrum is what function groups exist within the molecule.