SLOW DYNAMICS OF WATER-MOLECULES IN CONFINED SPACE

We present results of the analysis of quasi-elastic and inelastic inco herent neutron scattering of H2O contained in pores of Vycor glass. At room temperature and 50% hydration, the single particle motions of wa ter molecules can be described as a series of short time jump diffusio ns in a confined space of 5 angstrom with a residence time tau0 of 8 p s. As the temperature is lowered the residence time increases rapidly to 19 ps at -15-degrees-C. However, the translational diffusion consta nt is similar to the corresponding bulk value at each temperature. The peaks in the density of states for the translational motions as well as for the librational motions are slightly up-shifted compared to tha t of bulk water due to the confinement near the surface.