A hexaether-substituted rufigallol mesogen is studied by measuring deuteron spin-lattice relaxation times T-1Z and T-1Q in the hexagonal D-ho phase. Small-step rotations of discotic molecules within each column are described by the so-called 'anisotropic viscosity' model, giving rotational diffusion constants D-alpha and D-beta for rotations of the disc normal around and perpendicular to the director. A libration model is used to describe the wagging motions in different side chains as seen by the first CD bonds, which diffuse in a circular arc within a defined apex angle. The chain libration rates and corresponding apex angles are also derived. (C) 2003 Elsevier Science B.V. All rights reserved.