A molecule absorbs radiation when the natural frequency of vibrations of some part of a molecule is the same as the frequency of incident radiation.CRITERIA/ REQUIREMENTS FOR A COMPOUND TO ABSORB IR RADIATION:.Therefore, IR spectrum of a chemical substance is a finger print of a molecule for its identification.Hence gives the characteristic peak value. Different functional groups absorb characteristic frequencies of IR radiation.Then, absorption of IR radiation takes place & a peak is observed.When energy in the form of infrared radiation is applied then it causes the vibration between the atoms of the molecules & when,Īpplied infrared frequency= Natural frequency of vibration.The energy of molecular vibration is quantized.This characteristic vibration is called Natural frequency of vibration.In any molecule, movement of atoms & chemical bond is like spring & balls (vibration).Molecules are made up of atoms linked by chemical bonds.No 2 compounds except the enantiomers can have the similar IR spectra.Arrangement of the atoms within the molecule Mass of the atoms present in a moleculeģ. In IR spectroscopy the changes in the vibrational energy depends upon:ġ.The transitions which are not accompanied by a change in dipole moment of the molecule are not directly observed & are considered as IR inactive transitions.All the bonds in a molecule are not capable of absorbing IR energy but those bonds which are accompanied by a change in dipole moment will absorb in the IR region & such transitions are called IR active transitions.Therefore the IR spectroscopy is also called as ‘vibrational-rotational spectroscopy’.Each vibrational level is associated with a number of closely placed rotational level.Absorption of IR radiation causes an excitation of molecule from a lower to the higher vibrational level.When the frequency of the IR radiation is equal to the natural frequency of vibration, the molecule absorb IR radiation.The principle of IR spectroscopy is related to the vibrational & rotational energy of a molecule.IR radiation shows only rotational & vibrational level.Energy of radiation is directly proportional to wavenumber & inversely proportion to wavelength.It measures the bond vibration frequencies in a molecule.It is based on the absorption spectroscopy in which molecular vibration is observed due to absorption of IR radiation.Infrared radiations refers broadly to that part of electromagnetic spectrum between visible & microwave region.IR radiations lies in the wavelength range of 0.7-400 μm.It is an important qualitative analytical technique for determining the structure of both organic & inorganic compounds.The IR spectroscopy concept can be generally analysed in 3 ways:.Vibrations in IR spectroscopy also known as fundamental vibrations.It is also called as vibrational spectroscopy.Study of interaction between infrared radiations & matter. light having a longer wavelength & a lower frequency than visible light), which results in vibrational transitions i.e. Infrared spectroscopy is the spectroscopy which is concerned with the study of infrared region of electromagnetic spectrum (i.e.Spectroscopy is the branch of science dealing with the study of interaction of electromagnetic radiation with matter.
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