The process in which electromagnetic radiation is deflected by particles in the matter through which it passes. In elastic scattering the photons of the radiation are reflected; i.e. they bounce off the atoms and molecules without any change of energy. In this type of scattering, known as Rayleigh scattering (after Lord Rayleigh), there is a change of phase but no frequency change. In inelastic scattering and superelastic scattering, there is interchange of energy between the photons and the particles. Consequently, the scattered photons have a different wavelength as well as a different phase. Examples include the Raman effect and the Compton effect. See also Tyndall effect.