HIGH-RESOLUTION H-1-NMR IN SOLIDS WITH FREQUENCY-SWITCHED MULTIPLE-PULSE SEQUENCES

A new pulse sequence for abundant-spin NMR in solids, called FSLG240W, is demonstrated. The sequence employs phase-coherent frequency-switch ing of the rf irradiation to induce opposite rotations around the magi c-angle axis in the rotating frame. Three 4pi/3 rotations in one sense are followed by three 4pi/3 rotations in the opposite sense. Observat ion windows separate each rotation. The pulse sequence cancels out the average dipolar Hamiltonian, the first-order correction terms, and th e most deliterious second-order terms. The pulse sequence has a short cycle time and a high scaling factor kappa = 1/square-root 3, but is s ensitive to rf inhomogeneity. We demonstrate slightly better resolutio n than either MREV8 or BR24 on a small spherical sample of L-alanine.