Explain the theory of IR spectroscopy and its applications in biology in detail.
Spectroscopy is the analysis of the interaction between matter and any portion of the electromagnetic spectrum. It involves any interaction between light and matter, such as absorption, emission, and scattering.
Infrared (IR) spectroscopy is an important analytical technique for determining the structure of both inorganic & organic compounds. It is also known as vibrational spectroscopy. IR radiations lies in the wavelength range of 0.7 - 400 µm. IR spectroscopy is based upon selective absorption of IR radiations by the molecule which induces vibration of the molecules of the compound. IR instruments are of 2 types namely, dispersive instruments (spectrophotometers) and Fourier transform IR instrument. The radiation sources used are incandescent lamp, Nernst glower etc., and the detectors used are thermal and photon detectors.
Principle of IR spectroscopy:
When the energy in the form of IR is applied and if the applied IR frequency = Natural frequency of vibration, the absorption of IR takes place and a peak is observed. Molecules are excited to the higher energy state from the ground state when they absorb IR radiation. When a compound is exposed to IR radiation, it selectively absorbs the radiations resulting in vibration of the molecules of the compound, giving rise to closely packed absorption bands, called as IR absorption spectrum. The bands correspond to the characteristic functional groups and the bonds present in a chemical substance. Thus, an IR spectrum of a compound is considered as the fingerprint for its chemical identification.
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