The rectangular potential well (hat) model: application to the dielectric spectra of non-associated polar liquids

A theory of the wideband dielectric response of polar molecules in a hat-like rectangular well potential with perfectly elastic (reflecting) conical surface of finite depth is presented. The well represents molecular interaction in terms of the mean-field potential. Thus, escape of dipoles across the potential barrier, so they may execute complete rotations outside the cone, is also accounted for. This model is a generalisation of the cone-confined rotator and hybrid models, described previously by Gaiduk and Tseitlin [Adv. Chem. Phys. 87 (1994) 125; Mendeleev Commun. 1997, No. 2, p. 76]. In this work it is shown that the model, in which both the bottom of the potential well and its rim are flat, so that it resembles a hat, provides an adequate description of the wideband spectrum (comprising the Debye relaxation and far infra-red regions) of orientational polarisation. The applicability of the hat model has been demonstrated for strongly absorbing liquids, such as methyl chloride, for which wideband dielectric spectra due to molecular reorientation were calculated in the [0, THz] frequency region.