Experimental determination of the nature of diffusive motions of water molecules at low temperatures

Extensive and high-quality quasi-elastic incoherent neutron scattering data were obtained for water in the temperature range extending from room temperature down to -20 ^ in the supercooled state. The analysis generally confirms findings of our previous experiment S. H. Chen, J. Teixeira, and R. Nicklow, Phys. Rev. A 26, 3477 (1982), but in particular three new results have been obtained: (a) two relaxation times are clearly identified, which are related to the short-time and intermediate-time diffusion of water molecules, respectively, and their temperature dependence has been determined; (b) one of these relaxation times is associated with jump diffusion of the protons, and the temperature dependence of the jump length has been qualitatively determined; (c) the Q dependence of the scattering intensity integrated over the quasi-elastic region gives a Debye-Waller factor which is temperature independent.