%0 Journal Article %J Journal of Chemical Physics %D 1996 %T Second-order recoupling of chemical-shielding and dipolar-coupling tensors under spin decoupling in solid-state NMR %A Ernst, M. %A Bush, S. %A Kolbert, A. C. %A Pines, A. %K waltz-16 %X

The source of the residual line broadening in continuous-wave (cw) decoupled spectra under magic-angle sample spinning conditions is reexamined. It is shown that an important contribution to the line broadening comes from a second-order recoupling of the heteronuclear dipolar-coupling tensor and the chemical-shielding tensor of the irradiated spin. Such an interference between the two tensors leads to a sum of a zeroth-rank, a second-rank, and a fourth-rank tensor component in the Hamiltonian. The zeroth-rank and the fourth-rank tensor components are not averaged out under magic-angle sample spinning (MAS) conditions, requiring the use of higher-order averaging such as double rotation (DOR) for obtaining narrow lines. This broadening is distinctly different from off-resonance decoupling effects which transform as a second-rank tensor and can be averaged out by MAS. The properties of this second-order recoupling as a source of structural information are explored, and the conditions for removing the broadening in systems with weak homonuclear dipolar-coupling networks are discussed. (C) 1996 American Institute of Physics.

%B Journal of Chemical Physics %V 105 %P 3387-3397 %8 Sep 1 %@ 0021-9606 %G English %U ://WOS:A1996VD76800005 %N 9 %M WOS:A1996VD76800005 %! Second-order recoupling of chemical-shielding and dipolar-coupling tensors under spin decoupling in solid-state NMR %R Doi 10.1063/1.472224