ANALYTIC SOLUTIONS FOR THE TIME EVOLUTION OF DIPOLAR-DEPHASING NMR SIGNALS

The time evolution of dipolar-dephasing NMR signals reveals the streng th of dipolar couplings in solids. In most instances where microcrysta lline samples are investigated, numerical simulations of dipolar-depha sing intensities provide fits to experimental data in order to determi ne internuclear distances, In this paper, analytic solutions are deriv ed for the time evolution of signals in heteronuclear SEDOR, REDOR, an d TEDOR experiments. These solutions, in terms of infinite series of B essel functions of the first kind, are exact and replace a numerical i ntegration over the possible orientations of the internuclear vectors in a powdered or amorphous sample. Results from the analytic solutions converge rapidly and are compared here with results from numerical in tegration. A method for efficient least-squares fitting of dipolar-dep hasing data is also demonstrated, including fits to experimental SEDOR and TEDOR dephasing curves. (C) 1995 Academic Press, Inc.