Comparison of the coherence-transfer efficiencies of laboratory- and rotating-frame experiments

Coherence transfer under INEPT and isotropic mixing is quantified theoretically and the predictions are verified by experiments on various homonuclear spin systems. A general expression for magnetization transfer is derived for INEPT in A_MX_N systems, in terms of the “leaving fraction,” trigonometric function, “spin multiplier,” and “attenuation factor.” In general, coherence transfer under INEPT is not identical from A_M to X_N and X_N to A_M when M ≠ N. Unlike INEPT, in the case of isotropic mixing all magnetization components are conserved for the spin system as a whole, transfer is in-phase, and the m = 0 component of spin multiplets also plays a role in coherence transfer, leading to advantages over INEPT under conditions of unresolved couplings and integer composite angular momenta. Coherence-transfer efficiencies of these experiments are compared with the predicted universal bound on spin dynamics.