Higher-order dipole-dipole, dipole-quadrupole and field gradient contributions to the second light-scattering virial coefficient

Theory of the second light-scattering virial coefficient B p is extended to include in the scattered intensity terms that have not previously been considered, namely dipole-dipole intensities of the fifth power in the molecular polarizability α as well as additional contributions arising from field gradient effects and induced quadrupole moments in the molecular interactions. Numerical calculations for ten gases show that terms in α 5 make a significant contribution to B ρ of up to nearly 20%. In polar molecules, terms in α 2 A (where A describes the dipole induced by a field gradient, or the quadrupole induced by a field) make contributions of up to 9%. Indications are that in molecules with a centre of inversion, for which A is zero, field gradient and quadrupole effects will generally lead to contributions of less than 1%.