Workshop Report; Gases

The phenomena of absorption and scattering of light by atoms and molecules depend on the electric moments and polarizability of the absorbing or scattering entities. At low densities the entity is the individual molecule and a knowledge of the moments and polarizabilities of the single molecules is sufficient. In cases where interactions are important, new effects appear which depend not on the individual molecular properties, but on those of pairs or even clusters of molecules. In some systems these induced effects may even dominate the absorption (or scattering) spectrum; for example, absorption by molecules which individually have no permanent dipole moment.