A RAMAN INVESTIGATION OF ORIENTATIONAL DISORDER IN C-60

The different contributions which participate to the shift and broadening of an intramolecular mode in the plastic phase of C60 are recalled. Especially, using a rotational diffusion model, we calculate the expected step of the linewidth of the A(g) and H(g) Raman modes related to the slowing down of the reorientational process at the order-disorder phase transition. For H(g) modes a value of the order of 2 cm-1 is calculated. On the other hand, we have performed a detailed analysis of the temperature dependence of the Raman spectrum Of C60. We state that the slowing down of the reorientational process cannot explain alone the changes with temperature of the profile of the H(g) mode. We show that the room temperature spectrum of the 1426 cm-1 and 1575 cm-1 tangential H(g) modes results from the overlap of several components and the changes with temperature of the profile of the H(g) mode are mainly related to an opposite temperature dependence of the intensity of these components and not to a dramatic narrowing of these modes.