COMPUTATIONAL AND EXPERIMENTAL-STUDY OF NMR RELAXATION OF QUADRUPOLAR NOBLE-GAS NUCLEI IN ORGANIC-SOLVENTS

The spin-lattice relaxation times T1 of the quadrupolar noble gas nuclei Ne-21, Kr-83 and Xe-131 were measured in various solutions by applying the inversion-recovery method. The relaxation activation energies were determined from the temperature dependence of T1. Ab initio calculations were carried out in order to gain insight into the origin of the fluctuating electric field gradient (EFG) interacting with the nuclear electric quadrupole moment and (dominantly) causing the relaxation. The calculations, together with the experimental findings, clearly indicate the insufficiency of the electrostatic model, according to which the EFG arises from the charge distribution of the solvent molecules. Additional contributions to the EFG due to the deformation of the electron cloud of the solute atom have to be taken into account.