C₄-Rotational jumps in plastic adamantane the proof of their existence and uniqueness

Abstract

An extensive quasielastic incoherent neutron scattering study was performed on adamantane, C₁₀H₁₆, at 301 K and at 373 K, using a slab shaped single crystal. Multiple scattering corrections were carried out for three orientations of the sample with respect to the incident neutron beam. A suitable choice of the orientations and of the modulus of the momentum transfer vector Q together with the experimental energy resolution enabled us to distinguish between various rotational jump models and to prove that on the time scale of the experiment the only existing cubic rotations are of the C₄-type (90° rotational jumps of the molecules about fourfold symmetry axes of the crystal lattice). The corresponding correlation time is given by