NMR OF RESIDUAL PROTONS IN PARTLY DEUTERATED ANISOTROPIC MATERIALS WITH PHASE-ALTERNATED DECOUPLING OF DEUTERIUM SPINS

A new method is presented for decoupling spins with S = 1 like deuteri um in anisotropic media while observing other spins such as residual p rotons in partly deuterated samples. The carrier frequency of a weak r adiofrequency (RF) field is applied near the center of the doublet ari sing from the quadrupolar interaction of the S = 1 spins. The phase of the RF field is periodically reversed with intervals matching the rec iprocal of the magnitude of the quadrupolar splitting. It is shown by theory and experiment that, even when the irradiating field is quite w eak, the efficiency of this phase-alternated decoupling scheme is much better than for simple continuous-wave irradiation at the center of t he doublet, an established technique which is usually referred to as d ouble quantum decoupling. The phase-alternated experiment makes it pos sible to decouple large quadrupolar interactions with a weak RF field. A theoretical analysis and numerical simulations are presented to dem onstrate the decoupling performance. Proton spectra of partly deuterat ed dibromobutane in a liquid crystalline solvent have been recorded to illustrate the efficiency of phase-alternated deuterium decoupling.