On external dipolar relaxation in a two-spin system

Relaxation in an AB system, due to intermolecular dipole-dipole interaction is considered. The treatment implies a many-particle spin density matrix assuming its factorization. A critical analysis of the random local field (RLF) model is given. Relaxation coefficients of the AB system are evaluated for two cases: (1) external relaxation due to interaction with an equivalent spin system; (2) relaxation caused by intermolecular interaction of identical AB systems. Relaxation times are given for two simple models of the motion of spherical molecules: (1) an independent motion model and (2) a ‘solvation shell’ model.