Experimental characterization of intermolecular multiple-quantum coherence pumping efficiency in solution NMR.

The behavior of intermolecular multiple-quantum coherences in a variety of simple liquids with different chemical and magnetic properties is investigated experimentally and modeled by numerical simulations based on modified Bloch equations. The effects of spin concentration, temperature, intramolecular conformational flexibility, chemical exchange, and spin-spin coupling on the formation of high-order coherences are examined. It is shown that any process that makes the Larmor frequency time-dependent may interfere with the formation of these coherences. Good agreement is achieved between experiments and simulation, using independently known values of the magnetization density, the rate constants for translational diffusion, spin-spin and spin-lattice relaxation, and radiation damping.