Rotational motion of molecules in plastic neopentane

An isotropic rotational diffusion model is derived including continuous as well as jump-like diffusion of the molecular orientation. This theory gives good agreement with quasielastic neutron scattering data of plastic neopentane. Diffusion constants are obtained for both types of motion. The activation energy for large angle reorientations is determined as E_j = 0.81 ± 0.10 kcal/mole.