¹⁷O NMR Investigation of Water Structure and Dynamics

Abstract

The structure and dynamics of the bound water in barium chlorate monohydrate were studied with ¹⁷O nuclear magnetic resonance (NMR) spectroscopy in samples that are stationary and spinning at the magic-angle in magnetic fields ranging from 14.1 to 21.1 T. ¹⁷O NMR parameters of the water were determined, and the effects of torsional oscillations of the water molecule on the ¹⁷O quadrupolar coupling constant (C[subscript Q]) were delineated with variable temperature MAS NMR. With decreasing temperature and reduction of the librational motion, we observe an increase in the experimentally measured C[subscript Q] explaining the discrepancy between experiments and predictions from density functional theory. In addition, at low temperatures and in the absence of ¹H decoupling, we observe a well-resolved ¹H-¹⁷O dipole splitting in the spectra, which provides information on the structure of the H₂O molecule. The splitting arises because of the homogeneous nature of the coupling between the two ¹H-¹⁷O dipoles and the ¹H-¹H dipole.