Proton spin-lattice relaxation dispersion has been carefully measured at the Larmor frequency range from 3 kHz to 4 MHz in the smectic-C mesophase of 4-4′-bis-heptyloxy-azoxy-benzene (HpAB). Measurements were carried out by means of the fast field cycling NMR technique. The stability and precision of the low relaxation magnetic field has been tested by scanning the proton resonance with a second irradiation frequency. Three chemically inequivalent nitrogen nuclei have been detected, denoting the existence of two nonequivalent molecules. We conclude that a bimolecular structure can be associated with the elemental liquid crystalline unit.

• Received 11 September 1996

DOI:https://doi.org/10.1103/PhysRevE.55.7079