Spin relaxation in isolated and coupled non-integer quadrupolar nuclei: Theory and application for I = 3/2 nuclei

Abstract

A theoretical approach for the description of NMR experiments of non-integer quadrupolar nuclei undergoing molecular motion is presented. The approach is very general and can be extended to any other spin system. Here, various magnetic interactions (first and second order quadrupolar contributions, chemical shift anisotropy, dipole-dipole interactions) are taken into consideration as well as the effect of finite rf pulses. Model simulations are presented that demonstrate the influence of the magnetic interaction parameters, finite pulse effects and various motional models (2-, 3-, 4- and 12-site jump processes) on the NMR lineshapes, including central and satellite transitions, and relaxation data of isolated and coupled I = 3/2 nuclei. It is demonstrated that the various interactions and motional parameters have a strong impact on the expected NMR observables. An experimental example from ongoing ¹¹B NMR investigations, for which this theoretical approach will be useful, is briefly discussed.