Diffusional dynamics of hydrogen-bonded liquids: methanol

Medium-resolution ( Delta E approximately=0.1 meV) quasielastic neutron scattering spectra have been measured for partially (CD 3 OH) and fully deuterated methanol, (CD 3 OD) in the temperature range between 200 and 300 K. The spectra are analysed in terms of a simplified model which takes into account both coherent and incoherent contributions, and includes translational and rotational motions of the molecular frame as well as the rapid reorientation of the CD 3 group. Such a procedure enabled the separation of the translational and rotational contributions to the measured intensity. The apparent lack of saturation of the translational linewidths versus the momentum transfer is finally discussed in terms of a phenomenological stochastic model.