Computational and experimental study of NMR relaxation of quadrupolar noble gas nuclei in organic solvents

Abstract

The spin-lattice relaxation times T ₁ of the quadrupolar noble gas nuclei ²¹Ne, ⁸³Kr and ¹³¹Xe were measured in various solutions by applying the inversion-recovery method. The relaxation activation energies were determined from the temperature dependence of T ₁. 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.