The rotational diffusion of molecules in the liquid and solid states can be studied by radiation scattering experiments. Both neutron and light scattering data are interpreted, conventionally, on the basis of rotation of single molecules, although in dense systems cooperative rotation is a possibility. It is pointed out that a comparison of incoherent neutron data and depolarized light data allows the cooperative nature of molecular rotational diffusion to be verified. The method is applied to the plastic crystal phase of cyclohexane, and it is shown that individual molecules rotate about 10 times as rapidly as the relaxation rate of the mean orientation of a group of molecules.
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