ATR FT-IR spectroscopy is a method to obtain information about chemical bonding interactions based on absorption of infrared radiation (mid-infrared 2.5–25 μm), related to the fundamental vibrations of chemical bonds. A requirement to absorb IR radiation for a vibration mode of a molecule is a periodic change in the dipole moment of the molecule.  Discrete excitation energies of individual vibration modes can be related to the presence or absence of specific functional groups to determine the resultant surface chemistry as well as the chemical structures of thin films, composites and polymers

To obtain the required information, an infrared beam (IR beam) is directed at an optically dense crystal with a high refractive index (n>2) at a set angle. Internal reflections occur at the interface between crystal and specimen, creating evanescent waves propagating into the specimens held in contact with the crystal by a defined force. Absorption of radiation by the specimen correlates with an attenuate of the evanescent wave and an interference of the IR beam emerges the crystal. The interferogram signal collected by the detector is then Fourier-transformed to obtain an IR-spectra.