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Mid-infrared spectroscopy (MIR) is a vibrational spectroscopy technique that identifies chemicals based on the interaction of molecules with electromagnetic radiation in the mid-infrared region (400-4000 cm-1). Infrared spectroscopy identifies chemicals based on the absorption of specific wavelengths of mid-infrared light by a molecule. Molecular absorbances of mid-infrared light cause molecular rotations and vibrations and are classified by chemical functional groups. The resulting MIR spectrum produced is characteristic for a given molecule.

Infrared open-path systems send out a beam of infrared light through open air, detecting target gases along the path of the beam. This linear 'sensor' is typically a few meters up to a few hundred meters in length. Point analysis (“benchtop”) systems are used for analyzing condensed phase materials, although many systems are also capable of analyzing gases in gas cells. They are more common than open-path systems, and are found in a variety of sizes and capabilities.

Attenuated total reflection (ATR-MIR) is the most popular sampling technique used in most laboratories today, and allows for the fast analysis of solid and liquid materials. MIR spectra can be searched against large reference spectral databases, making this technique a powerful tool for identification of chemical unknowns.