NMR in Spinning Samples of Biaxial Liquid Crystals

Magnetic resonance measurements on a spinning sample of deuterated $n$-heptyloxyazozybenzene (HOAB-$d_{30}$) are presented. The resulting spectral patterns for the deuterated terminal methyl groups display the biaxial character of the smectic-$C$ phase. Values for those biaxial order parameters which survive under free molecular rotation are directly determined from the shape of the spectral patterns. Parameters expressing biased rotation are also present and contribute significantly to the biaxiality.