QNS investigation of restricted molecular reorientation in the nematic phase. I. The incoherent scattering law for MBBA

On the basis of the solution of the random flight problem of a particle between two perfectly reflecting potential barriers the incoherent scattering law for the model of the uniaxial, molecular stochastic reorientation within an arbitrary apex angle Ф₀ has been calculated. In conjunction with the published NMR results evidence is presented, that the along the long axis uniaxial rotation, can be described in terms of the model with an apex angle φ₀ of 57°. The model of the restricted uniaxial reorientation, which is expected to be of interest in nematic phases of biaxial molecules, has been applied to the investigation, by quasi elastic incoherent cold neutron scattering, of the rotational dynamics of the rigid benzylidene central part of a magnetically oriented MBBA sample in the nematic phase at 303 K.