LOCAL MOLECULAR ORDER IN THE BIAXIAL SMECTIC MESOPHASE OF HPAB - A PROTON-N-14 CROSS-RELAXATION STUDY

Proton spin-lattice relaxation dispersion has been carefully measured at the Larmor frequency range from 3 kHz to 4 MHz in the smectic-C mes ophase of 4-4'-bis-heptyloxy-azoxy-benzene (HpAB). Measurements were c arried out by means of the fast field cycling NMR technique. The stabi lity and precision of the low relaxation magnetic field has been teste d by scanning the proton resonance with a second irradiation frequency . Three chemically inequivalent nitrogen nuclei have been detected, de noting the existence of two nonequivalent molecules. We conclude that a bimolecular structure can be associated with the elemental liquid cr ystalline unit.