Studies of heteronuclear dipolar interactions between spin-1/2 and quadrupolar nuclei by using REDOR during multiple quantum evolution

A new technique for measurements of dipolar interactions in rotating solids is presented that combines the capabilities of multiple quantum magic angl e spinning (MQMAS) with the rotational echo double resonance (REDOR). It em ploys the dipolar recoupling between spin-1/2 (I) and quadrupolar (S) nucle i by applying a series of pi pulses to the I spins. In contrast to the prev iously reported MQ-REDOR method, the recoupling sequence is applied during the triple quantum, rather than single quantum evolution. As the dipolar ef fect is enhanced by the MQ coherence order, this new technique exhibits imp roved sensitivity toward weak dipolar interactions. (C) 1999 Elsevier Scien ce B.V. All rights reserved.