title: Homonuclear correlation experiments for quadrupolar nuclei, spinning away from the magic angle.
abstract: We present a set of homonuclear correlation experiments for half-integer quadrupolar spins in solids. In all these exchange-type experiments, the dipolar interaction is retained during the mixing time by spinning the sample at angles other than the "regular magic angle" (54.7 degrees celsius). The second-order quadrupolar interaction is averaged by different strategies for the different experiments. The multiple-quantum off magic angle spinning (MQOMAS) exchange experiment is essentially a regular MQMAS experiment where the quadrupolar interaction is averaged by combining magic angle spinning with a multiple- to single-quantum correlation scheme. The sample is spun at the magic angle at all times except during the mixing time which is added to establish homonuclear correlation. In the multiple-quantum P4 magic angle spinning (MQP4MAS) exchange experiment, the sample is spun at one of the angles at which the fourth-order Legendre polynomial vanishes (P4 magic angle), the remaining second-order quadrupolar interaction now governed by a second-rank tensor is refocussed by the multiple to single-quantum correlation scheme. In the dynamic angle spinning (DAS) exchange experiment, the second-order quadrupolar interaction is averaged by correlating the evolution from two complementary angles. These experiments are demonstrated and compared, in view of their specific advantages and disadvantages, for 23Na in the model compound Na2SO3.
authors.affiliation: Department of Physical Chemistry/Solid-State NMR, NSRIM Center, University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands.
authors.forename: T G
authors.initials: TG
authors.lastname: Ajithkumar
authors.forename: E R H
authors.initials: ER
authors.lastname: van Eck
authors.forename: A P M
authors.initials: AP
authors.lastname: Kentgens