Nonlinear dielectric relaxation spectroscopy has recently been utilized to investigate the details of electrical dynamics in a variety of substances. The nonlinear spectra obtained have usually been analyzed in terms of a phenomenological nonlinear response theory proposed by Nakada. In this paper, to check the validity of the phenomenological theory, the dielectric relaxation spectra of first and third orders are calculated from the molecular theory based on a free rotation model of the dipole moment. The after-effect function of exponential decay type assumed in the phenomenological theory is not applicable to the free rotation model. The validity of phenomenological expressions for nonlinear spectra as approximate or semiempirical formulas is discussed in detail.
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