Atoms or atomic groups in molecules are in continuous motion with respect to each other. These motions are twisting, bending, rotating and vibrational motions of atoms in a molecule. Upon interaction with infrared radiation, portions of the incident radiation are absorbed at particular wavelengths. These absorbed wavelengths are measured which are specific for particular atom present in a molecule. The multiplicity of vibrations occurring simultaneously produces a highly complex absorption spectrum which is uniquely characteristic of the functional groups comprising the molecule & of the overall configuration of the atoms as well.