Hydroxide-ion dynamics in cesium hydroxide: a deuteron nuclear magnetic resonance study

Abstract

CSOD exists in a number of solid phases that are distinguished by the different equilibrium positions and dynamics of the OD− ion. Deuteron nuclear magnetic resonance (NMR) was used as a probe because the observed quadrupolar split spectra provide a sensitive means of detecting changes in the symmetry properties of the unit cell and the motion of the O—D bond. Measurements are reported for the nuclear quadrupole coupling constant and the effective asymmetry parameter over the range from 100 to 500 K. The NMR data as well as differential thermal analysis confirm phase transitions from the cubic (Pm3m) to the high-temperature orthorhombic phase (Cmcm) at 497 K and a transition to a lower temperature phase at 247 K. The quadrupolar split spectra in the region from 497 to 247 K are consistent with a twofold reorientation of the O—D bond throughout this phase. The effective asymmetry parameter of the quadrupolar interaction increases rapidly with decreasing temperature, indicating a substantial change in the angle of reorientation. Below 247 K the spectra suggest that the motion of the OD− ion slows down on the time scale of the NMR line width (10−5 s).