FTIR PRINCIPLE
Principle of FTIR is based on the bonds and the groups of bonds vibrates at some characteristic frequencies. The molecule to be identified is exposed to the infrared rays. This molecule or a sample absorbs infrared energy at different frequencies which are the characteristic of the molecules. Dipole moment is produce by the differences of the charges in the electric field of its atoms. Now this molecules with dipole moment allows infrared photons to interact with the molecule causing excitation to higher vibrational states.Diatomic molecules due to equal electric fields of their atoms do not have a dipole moment.
During analysis of FTIR a spot or the specimen is subjected to a IR beam. The transmittance and reflectance of the infrared rays at different frequencies is translated into an IR absorption plot consisting of reverse peaks. The FTIR spectral pattern is then analyzed and matched with known signature of identified materials in the FTIR library. And hence the sample is matched with the known information and the unknown molecule is identified.