The orientation-dependent spin-lattice relaxation rates for biaxial li
quid crystal phases are given explicitly in terms of spectral densitie
s J(mLmL') (omega) described by Berggren et al. (1993, J. chem. Phys.,
99, 6180). It is recognized that the 'biaxial' spectral densities are
not observed in biaxial phases unless the director is oriented away f
rom the external magnetic field.