Molecular motions in compressed liquid water

Abstract

Proton and deuteron NMR spin–lattice relaxation times in liquid water and heavy water were measured as a function of pressure and temperature in the range 10–90°C and 1 bar–9 kbar. D2O was also studied at 150 and 200°C. Availability of density and viscosity data under these experimental conditions enabled us to separate the effects of temperature and density on the spin–lattice relaxation times, T1, and viscosities. Under the assumption that the intermolecular dipolar contribution to the proton T1 follows the changes in shear viscosity with temperature and density, we separated the intramolecular and intermolecular dipolar contributions to the proton T1. We found that at a temperature of 10°C the initial increase in density leads to faster reorientation of the water molecules. The effect was much smaller at 30°C. Analysis of the experimental data on H2O and D2O leads to the conclusion that compression diminishes the coupling between the rotational and translational motions of water molecules. The change in the nature of the rotation–translation coupling with increasing density is mainly responsible for the failure of the Debye equation to describe the density effects on the reorientation of water molecules. In the case of D2O we find a relatively small variation in the deuteron quadrupole coupling constant with increasing density. Its average value is approximately 230 kHz over the range of our experimental conditions. Another experimental finding of this study is the decrease in the activation energies for relaxation and shear viscosity with increasing density. All the experimental evidence indicates that compression of water leads to significant distortion and/or disruption of the hydrogen bond network with the important consequence that the dynamic behavior of water under high compression resembles more that of a ’’normal’’ molecular liquid of comparable molecular size. At high densities the hard core repulsive interactions begin to dominate over the directional interactions which are mainly responsible for the open structure of liquid water at low temperatures and pressures.

A reoptimization of the five-site water potential (TIP5P) for use with Ewald sums

“…3 That study used Ewald, which may be the reason for any small difference with our result of 1.58Ϯ0.5 ps. The TIP5P and TIP5P-E values are smaller than the experimental results, 66 indicating, along with the diffusion constant, faster dynamics. However, the value is closer to experiment than many models.…”

Simulations of ice and liquid water over a range of temperatures using the fluctuating charge model

“…Figure 4 shows this relaxation time, NMR , for the TIP4P-FQ model, the TIP4P model, 48 and from experiment. 116 The values of NMR are also given in Table I. Over the range of the experimental data, over 10°C, the agreement between experiment and the TIP4P-FQ model is good.…”

Diffusion and reaction pathways of water near fully hydrated TiO2 surfaces from ab initio molecular dynamics

“…S8 and S9 in the supplementary material). The simulation data are not accurate enough to discern between different relaxation models (e.g., exponential vs biexponential) but the correlation times are similar (∼5 ps) to those reported in NMR experiments of liquid water, 116 increasing slightly near the surfaces.…”