Infrared Spectroscopy (IR Spectroscopy) is a common spectroscopic technique used to analyze the functional groups of a sample by measuring its absorbency through different IR frequencies. IR spectrometers can accept a wide range of samples, including solid, liquids and gases. The infrared region of the electromagnetic spectrum can be divided into three regions, the near-, mid, and far- infrared. Near IR has a range of about 14000 cm-1, mid-infrared ranges from approximately 4000-400 cm-1, and far-infrared ranges from 400-10 cm-1. 
Infrared Spectroscopy essentially is a method used to identify functional groups of an unknown structure by varying vibrational activity. Infrared ‘light’ or radiation hits the bonds in the molecule, absorb the energy of the infrared light and respond by vibrating. This vibrating action can be anything from simple bending to stretching, rocking and scissoring. According to the amount of vibrational activity that occurs in the varying functional groups, the functional group is localized at a certain wavenumber that is calculated as inverse centimeters. Each functional group has a unique peak at certain wavenumbers. Essentially literature values of these functional groups can be used to help identify an unknown structure once put through an IR spectroscoper. Given peaks can be matched with literature values and a structure can be solved.
- Hsu, Sherman. "Infrared Spectroscopy." Handbook of Instrumental Techniques for Analytical Chemistry. Norwalk: Perkin-Elmer, n.d. 247-83. Www.prenhall.com. The Perkin-Elmer Corp. Web. <http://www.prenhall.com/settle/chapters/ch15.pdf>.