The net quadrupole interaction of the atomic nucleus is directly proportional to the superposition of the components of the irreducible electric field gradient tensor that are due to the various ionic charges and electric multipole moments of the molecules. Because of this, the symmetry of the distribution of the electric charges and electric multipole moments plays an important role in determining the quadrupole interaction and, consequently, the NMR relaxation times. If a water molecule rotates in-place, a similar effect occurs. Local order depends on the degree to which the water electric dipole moments are directed radially from the ion, on the similarity of the dipole-ion distances, and on the regularity of the tetrahedron.
Similar consideration apply to the effects of external ionic charges.
Because the NMR frequency is given by the difference between energy levels, this term contributes to the width of the NMR line. This is done for all nuclei in the sample and the result is the summation over these nuclei. The simplest case is that of a nucleus constrained to the isotropic bulk liquid environment. Copyright 2000 University of Texas Southwestern Medical Center at Dallas, All Rights Reserved.