Fermi resonance

The Fermi resonance (after Enrico Fermi ) is a physical phenomenon of infrared spectroscopy. Molecules are rotated by means of IR radiation in an Excited vibrational state. The case absorbed energy is applied to a chart intensity against wavenumber.

An IR spectrum can be roughly divided into two major areas. In the wave number range greater than 1500 cm - 1 are stretching vibrations of the functional groups and harmonics in the area including the deformation vibrations. The skeletal vibrations of a molecule are, however, encouraged even at low wave numbers.

But this is also the area of the bending modes, which makes the band allocation of the localized vibration. Below 1500 cm - 1, however, often occur in gangs, which are assigned to any normal vibrations, but through combination vibrations. As a combination vibrations combinations of two or more normal modes are referred to absorb the corresponding combined frequencies. Most of these bands are much less intense than the normal vibrations. An exception is the case by chance have in the overtone and combination vibrations of the same frequency. In this so-called Fermi resonance is observed two bands of similar intensity that are unique to any vibration.

• Spectroscopy
• Enrico Fermi