Study of HF doped ice by pulsed NMR

The spin–lattice relaxation times of protons in HF doped ice I have been measured in the laboratory frame (T1) and in the rotating reference frame (T1ρ) as a function of temperature and HF concentration. An activation energy of 5.66±0.1 kcal/mole is found for both T1 and T1ρ for temperatures above −100°C, and 1.8±0.2 kcal/mole for T1 for temperatures between −100 and −200°C. In the range 10−6–10−4 HF/H2O molecular ratio, T−11 is approximately proportional to the 3/4 power of the concentration of HF. Analysis of the behavior of T1 vs temperature shows that the defects induced by HF are different from those that are T1 effective in pure ice and are probably the same as those effective in dielectric relaxation. At high HF concentrations, we suggest that the proton magnetization relaxes through dipolar interaction with diffusing fluorine nuclei. The concentration dependence of T1 may thus be a combination of three relaxation mechanisms: that intrinsic to pure ice, that which is dominant for moderate HF content, and that which dominates at high HF concentration.