Infrared spectroscopy
The atoms in molecules are in constant motion as the bonds stretch and bend.
Exposure of a molecule to infrared radiation having energy equal to the difference in energy between the ground state and an excited state results in absorption of the radiation and excitation to a higher energy state.
An infrared spectrum is obtained by exposing a molecule to light having a range of frequencies in the infrared region.
The energy range for the infrared radiation is commonly used as wavenumbers (ν) in cm–1.
These motions (collectively known as vibrations) have frequencies corresponding to the frequency of light in the infrared region of the electromagnetic spectrum. The available vibrational energy levels for any molecule depend on its structure (see diagram).
Exposure of a molecule to infrared radiation having energy equal to the difference in energy between the ground state and an excited state results in absorption of the radiation and excitation to a higher energy state.
See in the diagram that radiation of different energy (frequency) can be absorbed by the same molecule.
An infrared spectrum is obtained by exposing a molecule to light having a range of frequencies in the infrared region.
In absorption spectra peaks occur where absorptions are observed. The position of these peaks can be correlated with the presence of various structural features in the molecule.
The energy range for the infrared radiation is commonly used as wavenumbers (ν) in cm–1.
Wavenumbers are the number of waves per centimeter, which is the inverse of the wavelength (λ). This is equal to the frequency (c/λ) divided by the speed of light (c).