The p,T-dependence of the self-diffusion coefficient D for methanol, methan(2H)ol and ethanol has been studied between 150 and 450 K at pressures up to 250 MPa. The experiments were performed in strengthened high-pressure glass cells by the application of the nuclear magnetic resonance (NMR) spin-echo technique with pulsed magnetic-field gradients. Upon cooling, molecular mobility is strongly reduced, leading to a pronounced non-Arrhenius temperature dependence of D. Applying the rough hard-sphere model (Chandler) to our data, a dramatic decrease of the A-parameter with falling temperature is observed. This behavior indicates that attractive intermolecular interactions dominate translational mobility. The best description of the data is given by the empirical Vogel–Tammann–Fulcher (VTF) equation, with ideal glass transition temperatures T0, that are in excellent agreement with those obtained from calorimetric studies. The isotope effect for self-diffusion in methanol and methan(2H)ol increases from ∼5% at high temperatures to about 40% in the supercooled region. This drastic increase is assumed to originate from a difference in hydrogen bond strength of the isotopes, as has already been found for light and heavy water.

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A titanium autoclave for the determination of self diffusion coefficients by the pulsed field gradient spin‐echo method is described, that has been used in the temperature range between 200 and 500 K at pressures up to 600 MPa.—In a first series of experiments, melts of n‐alkanes with chain lengths between 16 and 154 carbon atoms were studied. The data are analyzed with modifications of the hard sphere model and tested against the Rouse‐ and reptation model.

With the nuclear magnetic resonance (NMR)-spin echo technique, self-diffusion coefficients D of anhydrous liquid HF and DF have been obtained between the melting pressure curve and 373 K at a maximum pressure of 600 MPa. The distilling apparatus, made entirely of fluoropolymers, and the titanium autoclave used for the measurements are described. The isobars of D show a pressure independent activation energy of 9.92 kJ/mol for HF and 10.3 kJ/mol for DF. Deviations from Arrhenius behavior at the lowest temperatures could be described by a VTF-equation. The isotherms of self-diffusion show a monotonic, but slight decrease with rising pressure. The isotope effect DHF/DDF rises from 1.05 at 373 K to 1.20 at 200 K, which can be explained by higher hydrogen bond energies in the deuterated liquid. These findings are compared to results from similar measurements on water as well as apolar substances and discussed with respect to the topology of the hydrogen bond structure in liquid HF. Results from recent Monte Carlo-simulations are included in the discussion.

The self diffusion coefficients D have been measured for a series of linear and branched alkanes between the melting pressure curve and 450 K at pressures up to 200 MPa. The experiments were performed in a strengthened glass cell by application of the pulsed field gradient technique. — The p, T dependence of the data is described by the rough hard sphere model (Chandler) and by the interacting sphere model (Speedy). — The measurements have been extended to binary mixtures of a long chain alkane (tetradecane) and 4 to 12% w/w methane. The addition of relatively small amounts of the lower alkane enhances significantly the translational mobility and reduces the p. T dependence of the self diffusion coefficients of tetradecane.