QUASI-ELASTIC INCOHERENT NEUTRON-SCATTERING STUDY OF THE ROTATIONAL-DYNAMICS OF THE WATER-MOLECULES IN ANALCIME

The rotational motion of the water molecules in analcime has been inve stigated by quasielastic incoherent neutron scattering. Reorientationa l times vary from 65 +/- 20 ps at 260 K to 26 +/- 3 ps at 370 K, and t he temperature dependence suggests an activation energy for reorientat ions of 780 +/- 200 K. Measurements of the temperature dependence of t he intensity of the elastic incoherent scattering indicate that there is no cooperative ordering at low temperatures, and that instead there is a gradual freezing-in of the motion of individual water molecules.