Comparison of 17O spin-lattice relaxation solid state NMR studies of pure and doped ices

This paper gives results from NMR experiments measuring the dynamics of proton motion in various ice samples. Specifically, we measure 17O spin-lattice relaxation rates (T1) for pure ice, and for HCl and KOH-doped ices. For pure ice, a plot of Ln 1/T1 vs. 1/T between 230 and 145 K gives activation energies for proton motion of 4.4 ± 0.1 kcal/mol (8.4 T) and 3.4 ± 0.1 kcal/mol (7.0 T). For the HCl-doped samples, an Arrhenius behavior is observed in the experimental temperature range, giving activation energies of 4.6 ± 0.1 kcal/mol (2 M) (8.4 T) and 4.4 ± 0.1 kcal/mol (0.9 M) (8.4 T). In contrast, the KOH-doped ice data does not behave in an Arrhenius fashion, rather, the molecular dynamics appear to speed up at lower temperatures for all concentrations of KOH-doped ices.