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Abstract
The results of quasielastic neutron scattering (QNS) experiments for nematic and smectic liquid crystals performed in different laboratories are reviewed and compared with results of dielectric relaxation studies. The fIR spectra for PAA and HOAB in the frequency range of 20–200 cm−1 are presented. α(v) values for the nematic and isotropic phases in the whole frequency range including the microwave and submillimeter regions are discussed in terms of the two-time model for molecular librations in the potential cage (confined rotator model). The model fits very well all the experimental data obtained from microwave, carcinotron and fIR techniques. Additionally it may explain the discrepancy between QNS and dielectric relaxation correlation times.