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

The spin-lattice relaxation times T1 of the quadrupolar noble gas nucl ei Ne-21, Kr-83 and Xe-131 were measured in various solutions by apply ing the inversion-recovery method. The relaxation activation energies were determined from the temperature dependence of T1. Ab initio calcu lations were carried out in order to gain insight into the origin of t he fluctuating electric field gradient (EFG) interacting with the nucl ear electric quadrupole moment and (dominantly) causing the relaxation . The calculations, together with the experimental findings, clearly i ndicate the insufficiency of the electrostatic model, according to whi ch the EFG arises from the charge distribution of the solvent molecule s. Additional contributions to the EFG due to the deformation of the e lectron cloud of the solute atom have to be taken into account.