title: Efficient triple-quantum excitation in modified RIACT MQMAS NMR for I=3/2 nuclei.
abstract: A new approach involving the creation of triple-quantum (TQ) coherences from both TQ and central transitions (CT) is investigated, in order to enhance the efficiency of triple-quantum excitation for I=3/2 nuclei. The RIACT excitation scheme, a soft pi/2 and hard spin-locking pulse, is shown to induce both adiabatic coherence transfer between CT and TQ coherences and TQ nutation. By combining the RIACT scheme with the presaturation of the satellite transitions, a significant improvement in the TQ excitation can be achieved mainly through enhanced CT polarization via the RIACT mechanism, in particular for nuclei with moderate to large quadrupole coupling constants (> or = 2.0 MHz). There also exists a nontrivial contribution from the TQ transition, which depends on the size of the quadrupole interaction.
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory and Department of Chemistry, University of California at Berkeley, Berkeley, California 94720, USA.
authors.forename: Kwang Hun
authors.initials: KH
authors.lastname: Lim
authors.forename: Thibault
authors.initials: T
authors.lastname: Charpentier
authors.forename: Alexander
authors.initials: A
authors.lastname: Pines