Analytic Solutions for the Time Evolution of Dipolar-Dephasing NMR Signals

The time evolution of dipolar-dephasing NMR signals reveals the strength of dipolar couplings in solids. In most instances where microcrystalline samples are investigated, numerical simulations of dipolar-dephasing intensities provide fits to experimental data in order to determine internuclear distances. In this paper, analytic solutions are derived for the time evolution of signals in heteronuclear SEDOR, REDOR, and TEDOR experiments. These solutions, in terms of infinite series of Bessel functions of the first kind, are exact and replace a numerical integration 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 integration. A method for efficient least-squares fitting of dipolar-dephasing data is also demonstrated, including fits to experimental SEDOR and TEDOR dephasing curves.