17O NMR relaxation measurements for investigation of molecular dynamics in static solids using sodium nitrate as a model compound

Abstract

¹⁷O NMR methods are emerging as a powerful tool for determination of structure and dynamics in materials and biological solids. We present experimental and theoretical frameworks for measurements of ¹⁷O NMR relaxation times in static solids focusing on the excitation of the central transition of the ¹⁷O spin 5/2 system. We employ ¹⁷O-enriched NaNO₃ as a model compound, in which the nitrate oxygen atoms undergo 3-fold jumps. Rotating frame ($T_{1\rho }$), transverse ($T_2$) and longitudinal ($T_1$) relaxation times as well as line shapes were measured for the central transition in the 280 to 195 K temperature range at 14.1 and 18.8 T field strengths. We conduct experimental and theoretical comparison between different relaxation methods and demonstrate the advantage of combining data from multiple relaxation time and line shape measurements to obtain a more accurate determination of the dynamics as compared to either of the techniques alone. The computational framework for relaxation of spin 5/2 nuclei is developed using the numerical integration of the Liouville − von Neumann equation.