ELIMINATION OF HIGH-ORDER TERMS IN MULTIPLE-PULSE NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY - APPLICATION TO HOMONUCLEAR DECOUPLING IN SOLIDS

A novel approach to the design of solid state nuclear magnetic resonan ce multiple pulse experiments is described. Based on time dependent pe rturbation theory the pulse cycle decoupling principle is extended to fifth order. Furthermore, by analyzing symmetry and commutator relatio ns for high order terms in the average Hamiltonian expansion we introd uce so-called z-rotational decoupling accomplished by concatenation of phase shifted pulse cycles. These fundamental tools prove extremely u seful for the development of multiple pulse techniques capable of elim inating undesired interactions to high order in the average Hamiltonia n expansion. The applicability of the methods is demonstrated by const ruction of homonuclear multiple-pulse decoupling methods which suppres s pure dipolar terms up to fifth order and cross terms between rf inho mogeneity and dipolar coupling to second order in the Magnus expansion . For the dipolar terms this represents an improvement by two orders o f magnitude compared to previous homonuclear decoupling sequences. Hig h order truncation decoupling sequences based on the BLEW-12 and magic sandwich pulse cycles are compared to state-of-the-art methods numeri cally and by preliminary experiments. (C) 1997 American Institute of P hysics.