Evidence of alkyl rotational mobility from comparison of PAA and PAP neutron quasielastic scattering data

We ask whether a model assuming a rotational diffusion of two molecular ''halves'', consisting of rigidly coupled alkoxy groups plus benzene rings, works for interpretation of QNS data. For PAA such a model seems to work almost perfectly for both the normal and the methyl deuterated nematic substance. For PAP, however, it gives a much too intense quasielastic component in the normal nondeuterated substance indicating that there exist interconformational motions in ethoxy group which falls within the QNS observation window. When convoluting the scattering law of this motion with that of the molecular ''halves'' one obtains an almost perfect agreement with the QNS experimental data.