FREQUENCY-SELECTIVE HETERONUCLEAR RECOUPLING IN ROTATING SOLIDS

In solid state nuclear magnetic resonance spectroscopy, several methods have recently been introduced for the purpose of restoring dipolar couplings into magic angle spinning experiments. These powerful techniques are useful for the measurement of internuclear distances and, more generally, for filtering and correlation experiments in noncrystalline materials. In the case of heteronuclear spins, the rotational echo double resonance experiment provides an elegant and practical approach to the spectrally nonselective reintroduction of dipolar interactions. In this article, we describe an approach to restore heteronuclear couplings which is spectrally selective-in particular we recouple the observed spins only with those nonobserved spins lying at exact resonance (and at multiples of the spinning frequency) in the triple resonance experiment. We refer to the technique as frequency-selective dipolar recoupling.