M. Eden et Mh. Levitt, Pulse sequence symmetries in the nuclear magnetic resonance of spinning solids: Application to heteronuclear decoupling, J CHEM PHYS, 111(4), 1999, pp. 1511-1519
We develop the average Hamiltonian theory of a class of symmetrical radio-f
requency pulse sequences in the NMR of rotating solids. Theorems are presen
ted which allow one to predict the elimination of many average Hamiltonian
terms, without detailed calculation. These results are applied to the probl
em of heteronuclear decoupling in the presence of rapid magic angle spinnin
g. We present sequences which minimize the number of heteronuclear terms at
the same time as recoupling the homonuclear interactions of the irradiated
spins. The performance of the new sequences is tested on C-13 labeled calc
ium formate. Experimental measurements of double-quantum H-1 excitation ind
icate a relationship between good heteronuclear decoupling of the observed
spin species and efficient recoupling of the irradiated spin species. The h
eteronuclear decoupling performance of the new sequences is significantly b
etter than that obtained with an unmodulated radio-frequency field. The dec
oupling performance is improved further by breaking the pulse sequence symm
etry in a controlled fashion. (C) 1999 American Institute of Physics. [S002
1-9606(99)00228-7].