Spectral densities from NMR relaxation data: A tracing procedure involving frequency-reduced variables

Abstract

A fairly direct statistical mechanical description of the motion of spins is given by the frequency dependence of the spectral density function. A method is described for determining the form of spectral density functions and their temperature dependence from measurements of motionally induced NMR relaxation rates. The method involves a simple tracing technique and utilizes measurements of T 1, T 1 ϱ , and T 2 over a range of temperatures. Measurement of T 1 at a large number of frequencies is not required. Analysis of representative relaxation data, taken from the literature, for eleven compounds is presented to illustrate the wide applicability of the technique. The resulting spectral densities are discussed in terms of recent theoretical work.