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 i

Molecular motions in compressed liquid water

Self‐diffusion coefficients and rotational correlation times have been measured in several polar liquids by pulsed nuclear magnetic resonance techniques. Diffusion coefficients were measured for HCCl3, ClC6H5, HF, and HCl and relaxation times for HF. The self‐diffusion coefficient of a liquid is related to the rotational correlation time τ2 by means of the quasilattice model of liquids. The rotational diffusion equation and the Stokes–Einstein expression for the rotational diffusion coefficient are inadequate and are respectively replaced by the results of the large‐step random‐walk theory of rotational diffusion and an expression for τ2 based on the quasilattice model. An expression for τ2, obtained from the dynamical rotational coherence theory, is shown not to apply in the case of the spherical‐top molecule CCl4 which would be anticipated to have a small friction constant. The correspondence between calculated values of τ2 based on the quasilattice model and the observed rotational correlation times is...

Self‐Diffusion Coefficients and Rotational Correlation Times in Polar Liquids

Results of high pressure study of the depolarized Rayleigh scattering in acetone, benzene, and methyl iodide are presented The density dependences of the angular velocity and angular position correlation functions are determined The angular velocity correlation function of each liquid shows a negative overshoot In addition, benzene at all pressures and methyl iodide at high pressures exhibit additional oscillations in the angular velocity correlation function The details of the correlation functions are discussed in terms of ''collision interrupted'' models such as the well known J‐diffusion model It is concluded that a more general description than J diffusion capable of allowing incomplete loss of momentum upon collision is needed The results are compared to studies of reorientation by means of NMR Finally, the relation between shear viscosity and reorientation in these liquids is discussed

Molecular reorientation in liquids by Rayleigh scattering: Pressure dependence of rotational correlation functions

The deuteron and nitrogen spin–lattice relaxation times of acetonitrile‐d3 have been measured as a function of pressure up to 2 kbar at 23°C using the NMR pulse method. Since the quadrupole coupling constants for nitrogen and deuterons in acetonitrile‐d3 are known, the experimental T1 data were interpretable in terms of the rotational diffusion constants for motion perpendicular and parallel to the symmetry axis, D⊥ and D‖, respectively. In agreement with our previous results the calculated activation volumes show that ΔV‡(D⊥) is much larger than ΔV‡(D‖).

Effect of Pressure on the Anisotropic Reorientation of Acetonitrile‐d3 in the Liquid State

A Monte Carlo simulation of liquid acetone was performed in the NVT ensemble. The dielectric polarizability of the molecules was taken into account by induced point dipoles. A reference simulation on a system of non-polarizable molecules was also carried out. The induced polarization of the molecules lowered the total energy of the system, while the sum of the pair interaction energies was increased. The structural analysis of the resulting configurations revealed that the average coordination number in the first coordination shell is about 12, and the first one or two nearest neighbours tend to be in an antiparallel orientation relative to the central molecule while the orientation of the rest of the neighbours is random. The predominant interaction in determining the structure of liquid acetone was found to be steric rather than electrostatic. The induced dipole moments of the molecules and the electric field strength at the location of the molecular centres were also examined. The induced dipole moment...

Monte carlo simulation of liquid acetone with a polarizable molecular model

The pressure dependence of the proton spin–lattice relaxation times has been measured at 23°C in liquid benzene and its mixtures with benzene‐d6 up to 600 bar, and in liquid chlorobenzene and its mixtures with chlorobenzene‐d5 up to 2000 bar. The separation of the intramolecular and intermolecular contributions to proton dipolar relaxation allowed us to study the effect of pressure on the reorientational and translational motions of the molecular liquids investigated. As predicted by the Bloembergen–Purcell–Pound (BPP) theory the intermolecular T1 were found to follow the changes in the viscosity with pressure. On the other hand, the experimental pressure dependence of the intramolecular T1 in benzene differs widely from the BPP theoretical prediction due to the relatively free rotation about the C6 axis in benzene. Removal of the C6 axis and introduction of a dipole in chlorobenzene result in agreement between theoretical and experimental intramolecular T1 pressure dependences. As an example of a molecul...

J. Jonas

Papers

Effect of Pressure on the Intramolecular and Intermolecular Contributions to Dipolar Spin Relaxation in Benzene and Chlorobenzene in the Liquid State