Efficient triple-quantum excitation in modified RIACT MQMAS NMR for I=3/2 nuclei.
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.
Lim
Kwang Hun
KH
Materials Sciences Division, Lawrence Berkeley National Laboratory and Department of Chemistry, University of California at Berkeley, Berkeley, California 94720, USA.
Charpentier
Thibault
T
Pines
Alexander
A