FTIR spectroscopy is a method for determining the structure of a material. FTIR stands for Fourier Transform Infra Red. Infrared refers to the part of the electromagnetic spectrum that lies between visible light and microwaves. We perceive some parts of the infrared range radiation as heat.
Now let's describe how FTIR spectroscopy works. An FTIR spectrometer consists of a source of infrared radiation, an interferometer, and a detector. All atoms and molecules vibrate at specific frequencies. When the frequency of infrared radiation matches the vibration frequency of an atom, molecule, or a group of atoms bonded together within a molecule (a so-called "functional group"), the infrared radiation will be absorbed. The amount of absorbed radiation depends on the strength of a bond. Each functional group absorbs its own unique frequency. So, if we measure absorbances of different frequencies of infrared radiation from a sample, we can obtain information about the chemical structure of the sample. A radiation source produces a broadband beam of infrared radiation. An interferometer converts the infrared beam into an interference signal (interferogram) containing all of the infrared frequencies. The interference signal goes to the sample, where some radiation is absorbed, and then to a detector. The final interferogram is then mathematically transformed (Fourier transformation) into an absorption spectrum containing the structural "fingerprint" of the sample.