Infrared (IR) Spectroscopy

Abstract

Infrared spectroscopy deals with the recording of the absorption of radiations in the infrared region of the electromagnetic spectrum. The position of a given infrared absorption is expressed in terms of wavelength in micron μ or more commonly in terms of wavenumber EquationSource% MathType!MTEF!2!1!+- % feaagCart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGafqyVd4Mbae % baaaa!37C4!]]</EquationSource><EquationSource Format="TEX"><![CDATA[$$ \bar \nu $$ (cm⁻¹) since it is directly proportional to energy. Note that wavenumbers are often called frequencies, although strictly it is incorrect. However, it is not a serious error as long as we keep in mind that EquationSource% MathType!MTEF!2!1!+- % feaagCart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGafqyVd4Mbae % bacqGH9aqpdaWcaaqaaiaaigdaaeaacqaH7oaBaaaaaa!3B49!]]</EquationSource><EquationSource Format="TEX"><![CDATA[$$ \bar \nu = \frac{1}{\lambda } $$ and ν = c/λ. The ordinary infrared region 2.5–15 μ (4000–667 cm⁻¹) is of greatest practical use to organic chemists. The region 0.8–2.5 μ (12,500–4000 cm⁻¹) is called the near infrared and the region 15–200 μ (667–50 cm⁻¹) the far infrared. The absorption of infrared radiation by a molecule occurs due to quantized vibrational and rotational energy changes when it is subjected to infrared irradiation. Thus, IR spectra are often called vibrational-rotational spectra.