Diffusive motions of water molecules near 1 °C

Abstract

Neutron (quasi-elastic) scattering experiments have been carried out to investigate the effects of temperature and pressure on the motion of molecules in liquid H2O. Spectra were obtained at several temperatures between −10 and +24 °C at atmospheric pressure, and also at +1 °Cand 1.42 × 108 Pa. The root-mean-square amplitude of proton motion in solid and liquid H2O at atmospheric pressure has been inferred from measurements of the Debye–Waller factor and is nearly constant at 0.07 nm for both the solid and liquid. A model in which the translational diffusion and rotational diffusion are based on Brownian motion was fitted to our data using published diffusion coefficient data. The structure breaking time was found to be very small at 1 and 10 °C. Both these conclusions are compared with those reported in several earlier papers, which gave varying results.The spectrum measured at 1.42 × 108 Pa was slightly broader than the corresponding spectrum at atmospheric pressure, probably indicating that the well-known minimum in the viscosity at this pressure is due to a structure breaking effect.