Orientational Order in Biaxial Liquid Crystals: The Smectic-VI and - H Phases

The ¹⁴N nuclear-quadrupole resonance (NQR) data of Seliger et al. on the smectic-VI and -H phases of terephtal-bis-butylaniline are reanalyzed and compared to neutron results. For the smectic-VI phase, both methods lead to remarkably consistent conclusions, but do not differentiate between possible models. For the H phase, the NQR results are consistent both with a model permitting weak orientational order around the long axis and with a model permitting uniform rotation around the long axis plus (anisotropic) fluctuations of this axis. The latter is more realistic since it agrees with the neutron results while the former does not.