DIELECTRIC RESPONSE AND A PHENOMENON OF A NARROW-BAND ABSORPTION FOR A CLASSICAL ROTOR IN A DOUBLE-WELL POTENTIAL

The theory of dielectric relaxation in a planar ensemble of polar mole cules is presented for a model where dipoles may rotate in a conservat ive double well potential (DWP) U = U-0 sin(2) theta. The evolution of wideband dielectric spectra as a function of the potential well depth U-0 is studied; both isotropic and anisotropic media being taken as e xamples. The spectra comprise the Debye relaxation and the quasiresona nt Poley absorption regions. The exact theory is compared with a simpl e quasielastic bond/extended diffusion approximation. The latter is va lid for a quantitative description for any value of the held parameter p=[U-0/(KBT)](1/2). For p much greater than 1 the spectrum comprises one narrow absorption band, while the Debye relaxation region is marke dly shifted to low frequencies. It is shown that in the long Lifetime tau limit there exists a minimum absorption band Delta nu(0)(p). The q uantity Delta nu(0) becomes small for values of parameter p much great er than 1. The dielectric relaxation in ice 1 is discussed in relation to this phenomenon. (C) 1995 American Institute of Physics.