P, T-DEPENDENCE OF SELF-DIFFUSION IN LIQUID-HYDROGEN FLUORIDE

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