NMR measurement of biaxial molecular order in the smecticCphase

Deuterium magnetic-resonance studies of spectral patterns from spinning samples are made to measure the relative contribution of various orientational order mechanisms to the biaxiality of the hydrocarbon chain in the smectic $C$ phase. The detailed theory of motional averaging as applied to the spinning techniques is reported for the first time. Orientational order parameters measurable by this technique representing various aspects of molecular orientational order are discussed. The technique is applied to a particular compound $n$-heptyloxyazoxybenzene, where it is possible to distinguish between those order parameter which result from rotational biasing about the long molecular axis and those order parameters which do not. The temperature dependence of these order parameters in this fixed-tilt-angle system is then determined.