A phenomenon of solutions of macromolecules; used analytically to determine the molecular mass and shape of a macromolecule from the effect on the intensity of scattered light of the wavelength of light and the angle of its scatter. In Rayleigh scattering the interaction of a photon with the molecule is elastic, i.e. there is no energy transfer from photon to molecule. In Raman scattering the interaction is inelastic, i.e. there is energy exchange, usually to vibrational energy (infrared) of the molecule, and the scattered light is then of longer wavelength.