GENERAL ORIENTATION DEPENDENCE OF NMR SPIN-LATTICE RELAXATION FOR SPIN-1

The theory of NMR spin-lattice relaxation of spin-1 nuclei relaxing via fluctuating quadrupolar interactions is considered within the Redfield approximation. The NMR spectrum is characterized in terms of the principal-axis coordinate system of the time-averaged electric-field gradient tensor. The most general form of the relaxation rates may be written in terms of the polar coordinates (β, α) of the magnetic field in the principal-axis coordinate system. It involves a sum of spherical harmonics up to order four, 1/Ti, = ∑4p=0 ∑pq=-pa(i)pqYpq(β, α), p even, where Ti represents T1z, T1q, and T2 and the a(i)pq values depend on reduced spectral densities and spherical order parameters which are independent of the orientation of the magnetic field. The number and types of order parameters required to characterize the orientation dependence of the relaxation rates depend on the symmetry of the motions as well as on the symmetry of the average electric-field gradient. Some examples of the use of the general theory are discussed. © 1993 by Academic Press, Inc.