Line-Shape Analyses of Solid-state 17O NMR Spectra for Hexagonal Ice

Abstract

We present the results of experimental and theoretical investigations of line shapes in solid-state 17O NMR spectra of hexagonal ice, Ih. Stationary 17O NMR spectra of Ih at temperatures from 143 to 280 K were obtained at 11.7 and 16.4 T. Line shapes changed drastically as the temperature was increased from 143 to 243 K; at 253 K and above, pseudo-isotropic line shapes appear, indicating the presence of reorientational motions. We find that Ratcliffe’s model, which involves twelve orientations and four-step jumps for water reorientational motions, is effective for analyzing the NMR spectra at temperatures below 243 K. The present analysis demonstrates that the isotropic line shapes arise from proton disorder with respect to the solid-state 17O NMR time scale, producing pseudoicosahedral motional averaging that can completely average out second-order quadrupole interactions.