Calculation of exchange-broadened NMR lineshapes II. Nuclear magnetic double resonance

Abstract

The general theory of exchange-broadened NMR Lineshapes developed by Binsch (1) is applied to the problem of the nuclear magnetic double resonance (NMDR) spectrum of an exchanging two-spin-1(2 system. Relaxation of the spin system is described by the theory of Redfield (2). Deviations from equilibrium population of the four energy levels are calculated for various combinations of parameters. The effect of the strong rf field on populations becomes qualitatively different if the exchange rate exceeds the relaxation rate. These population deviations are then used to calculate NMR Lineshapes for common experimental situations, including “tickling” and ”decoupling.” Measurement of exchange times may be more facile in the double resonance experiment than in the single resonance experiment. For intermediate exchange rates, the richer structure of the double resonance experiment would provide an easier comparison of calculated and experimental spectra. For small exchange rates comparable to the relaxation rate, the strongly decoupled spectrum would provide a ready measure of the exchange rate relative to the relaxation rate.