Rotational Brownian motion and nonlinear dielectric relaxation of asymmetric top molecules in strong electric fields.

A general theoretical treatment of the nonlinear dielectric response of an assembly of asymmetric top molecules in strong electric fields is presented in the context of the noninertial rotational diffusion model. The calculation proceeds by obtaining an infinite hierarchy of recurrence equations for the expectation values of Wigner's D functions describing nonlinear relaxation of the system. This hierarchy may be used for the evaluation of both transient and ac nonlinear responses in strong electric fields. The solution of this hierarchy is obtained for the particular case of rigid rodlike molecules in superimposed ac and strong dc bias electric fields, allowing one to evaluate the corresponding nonlinear response. The results are in agreement with available experimental data on nonlinear dielectric relaxation of dilute solutions of polar rodlike molecules in nonpolar solvents.