High resolution NMR studies of relaxation using saturation. Part II. Bandshape analysis for a nonequivalent two-spin system

Abstract

The bandshape for the NMR spectrum of a nonequivalent second-order two-spin system is discussed as a function of saturation. A comparison is made of the shapes predicted by two simple relaxation mechanisms, namely (i) isotropic random field relaxation and (ii) intramolecular dipolar relaxation. The effects of neglecting certain terms in the Redfield relaxation matrix are discussed with reference to these two mechanisms. It is shown that under conditions of saturation all terms in the relaxation matrix must be included. The Fourier analysis method of solving the simultaneous equations of motion of the density matrix is shown to give a factorization of the problem independently of arguments made about the nature of the relaxation process. A doped sample of 2-ehloroacrylonitrile is used as an experimental test case of the progressive saturation method. It is shown that this sample undergoes relaxation primarily of the random field type, as expected. Iterative lineshape fitting using the frill density matrix theory is discussed and all parameters characterizing the random field relaxation are obtained.