The dynamics of norbornane molecules is studied over the 120 K-348 K temperature range in its ordered (T < 131.5 K) and in its two orientationally disordered solid phases, using the incoherent quasielastic neutron scattering technique. On the time-scale accessible to time-of-flight neutron spectroscopy, (10–11 – 10–12 s), an elastic incoherent structure factor is extracted in the two plastic phases, which corresponds to isotropic rotations of the molecules about their centre of gravity, with apparently no change at the transition between the two phases. A description in terms of an isotropic rotational diffusion model yields a unique Arrhenius law for the diffusion constant through all the temperature range of these two phases. A more sophisticated description based on reorientations about lattice and molecules axes gives a continuous evolution of the correlation times across the transition. A comparison is made with recent NMR results. At the lowest temperatures in the h.c.p. plastic phase, an extra amount of elastic scattering is evidenced. A possible interpretation in terms of either a local ordering of the molecules or a distribution of the correlation times is proposed
