Infrared spectroscopy and vibrations
Atoms joined by covalent bonds are not permanently fixed in one position but undergo continual vibrations relative to each other. The energies associated with these vibrations correspond to absorption in the infrared region of the electromagnetic spectrum: wavelength (λ) 3 × 10−6 to 3 × 10−3 m; frequency (γ) range 1014 to 1011 Hz; energy range (E) 4 × 10−1 to 4 × 10−2 kJ mol−1.
There are many types of vibrations: symmetric and asymmetric stretching, scissoring, rocking, wagging, twisting and bending. An infrared spectrum of a molecule indicates the frequency range (peaks/bands) (expressed in wavenumbers, cm−1) over which characteristic absorption occurs and these are used to identify the presence of particular bonds or groups of atoms present.