Supercycled symmetry-based double-quantum dipolar recouplingof quadrupolar spins in MAS NMR: I. Theory

摘要

Using average Hamiltonian (AH) theory, we analyze recently introduced homonuclear dipolar recouplingpulse sequences for exciting central-transition double-quantum coherences (2QC) between half-integerspin quadrupolar nuclei undergoing magic-angle-spinning. Several previously observed differencesamong the recoupling schemes concerning their compensation to resonance offsets and radio-frequency(rf) inhomogeneity may qualitatively be rationalized by an AH analysis up to third perturbation order,despite its omission of first-order quadrupolar interactions. General aspects of the engineering of 2Q-recoupling pulse sequences applicable to half-integer spins are discussed, emphasizing the improve-ments offered from a diversity of supercycles providing 'enhanced suppression of undesirable AHcross-terms between resonance offsets and rf amplitude errors.