Extended rotational diffusion and dielectric relaxation in a constant external electric field

The complex dielectric-susceptibility tensor and spectra of the molecular dipole-moment autocorrelation matrix are calculated for a system of noninteracting linear molecules located in a constant external electric field. Calculations were carried out in the context of the extended rotational-diffusion (J-diffusion) model. Sum rules for the integrated absorption are derived. Results are compared with those for magnetic relaxation of fine ferromagnetic particles in a ferrofluid and to available experimental data.