Rayleigh scattering (no change in excitation wavelength) is differentiated from Stokes and anti-Stokes radiation. Rayleigh scattering occurs when an elastic collision takes place between an incident photon and an electron. The electron is raised to a short-lived higher energy level by energy absorption and finally falls back to its base level by releasing the same energy. If the photon excites an oscillation, vibration or rotation, a part of the energy is transferred to the atom/molecule. It therefore remains at an energetically higher state, which means that only part of the radiated energy is released again. This is called Stokes-scattering. The wavelength of this scattering is usually given as the difference to the wavelength of the excitation radiation in wavenumbers (cm-1). When an already existing oscillation gives its energy to the incident photons, involved electrons fall back to the ground level. In this case, we speak of anti-Stokes scattering, whose wavenumber results from the involved energy levels in sum to the excitation wavelength. In the wavenumber spectrum, Stokes and anti-Stokes are arranged axisymmetrically with respect to the Rayleigh wavelength (corresponding to 0 cm-1) and are specific for the present form of chemical bonds. Thus, molecular bonds can be identified on the basis of a Raman spectrum.