Measurement by NMR of the Diffusion Rate of HF in Ice

Abstract

An experiment is described by which the diffusion of fluorine in monocrystalline ice cylinders is followed quasicontinuously, using the proton magnetic resonance spin—lattice relaxation time T₁ to measure the HF concentration along the sample. The diffusion coefficient D_F was evaluated for various temperatures between −30° and −4°C. The results show more scatter than the experimental error can account for. A least‐squares fit of our data yields D_F (−10°C)=0.8×10⁻⁶ cm²/sec for the diffusivity and E=0.58 eV=13.4 kcal/mole for the activation energy, with root‐mean‐square deviations of 0.5×10⁻⁶ cm²/sec and 0.08 eV, respectively. We find that the highest concentration of diffused HF which can be absorbed by monocrystalline ice is about 4×10⁻⁵ HF/H₂O. A possible explanation is offered for the large value and dispersion of the diffusivity.