Infrared (IR) spectroscopy is a part of the electromagnetic spectrum which exist between visible and microwave regions. The IR range occurs between 0.78 um to 1000 um. It is divided into three regions, i.e., near that lies between 0.78 to 2.5 um, middle between 2.5 to 15.4 um and far between 15.4 to 1000 um.
Near IR region is generally used for quantitative analysis of low molecular weight hydrocarbons, water, and proteins. Middle IR region is mostly used for spectral analysis which causes vibrational and rotational energy changes helps in determination of organic structure based upon the absorption spectra. Far IR region is used generally for organo-metallics, it helps in quantitative analysis of bromides and chlorides of higher band frequencies. The mid-IR region is further divided into group frequency region, fingerprint region, and aromatic region.
When IR radiations are absorbed, it leads to energy changes of the order of 8-40 KJ/mole. The IR energy absorbed cause bonds in the molecule to stretch and bend in the covalent molecules. This helps in the identification of an unknown compound, as a spectrum of the authentic sample is matched with an unknown sample. It is not just for identification, but mainly it helps to determine structural information for a molecule, i.e., bond and type of functional groups example vibrational frequency 3000± 1500 cm-1 is for C-H bond and 1715±100 cm-1 is for carbonyl group.