Rotational diffusion in para-azoxyanisole

Abstract

Dielectric susceptibility (ε′, ε″) measurements were made on isotropic, nematic, and solid para-azoxyanisole in the micro-wave region. From the Cole-Cole plots, dielectric relaxation times were determined and the barrier-to-rotation, interpreted as corresponding to rotation around the long molecular axis, was estimated to be 2.6 kcal/mol in the isotropic phase and 2.3 kcal/mol in the nematic phase. In the solid phase ε′ drops to low values practically equal to ε_∞.

Infra-red measurements were performed additionally for the solid substance. From the temperature dependence of the peak widths at 910 cm^–1(benzene rings), 1020 cm^–1(O—CH₃ groups), and 1330 cm^–1(N₂O group) the corresponding barriers-to-rotation were found to be 1.9, 1.9 and 4.5 kcal/mol respectively.

The possible influence on neutron quasielastic scattering measurements is discussed.