A very high resolution incoherent quasi-elastic neutron scattering study of the smectic e, b and a phases of deutero n-butyl 4-(4’-phenylbenzylideneamino)cinnamate (d-bpbac)

Incoherent quasi-elastic neutron-scattering spectra have been measured on powder samples of D-BPBAC in its smectic E, B and A phases using the high-resolution backscattering technique. The data have been analysed in terms of translational diffusion and a localized rotational motion. It has been found that the apparent translational diffusion constant has a temperature dependent value of ~1 x 10^-6 cm² s^-1 in the smectic A phase but is smaller by at least an order of magnitude in the smectic B and E phases. Comparison of the widths of the rotational components of the spectra with other measurements suggests that simple rotational models are not adequate to explain the experimental data.