Isotropic second-order dipolar shifts in the rotating frame

TitleIsotropic second-order dipolar shifts in the rotating frame
Publication TypeJournal Article
Year of Publication1996
AuthorsErnst M., Kolbert A.C, Schmidt-Rohr K., Pines A
JournalJournal of Chemical Physics
Date PublishedJun 1
ISBN Number0021-9606
Accession NumberWOS:A1996UM90900008

An experiment is described that utilizes the truncation of the Hamiltonian in the rotating frame by a radio-frequency field designed to yield an isotropic shift for the dipolar coupling. This approach allows the measurement of a normally orientation-dependent coupling constant by a single isotropic value. The dipolar isotropic shift is closely related to the field-dependent chemical shift in solids due to the second-order dipolar perturbation observed in magic-angle spinning experiments. In the rotating frame, larger shifts of up to 1000 Hz can be observed for the case of a one-bond C-H coupling compared to a shift of a few Hertz in the laboratory-frame experiment. In addition to the isotropic shift, a line broadening due to the P-4(cos beta) terms is observed when the experiment is carried out under magic-angle sample spinning (MAS) conditions, leading to the requirement of higher-order averaging such as double rotation (DOR) for obtaining narrow lines. As an application of this new experiment the separation of CH, CH2, and CH3 groups in a 2D spectrum under MAS is demonstrated. Implemented under DOR it could be used as a technique to select carbon atoms according to the number of directly attached protons. (C) 1996 American Institute of Physics.

URL<Go to ISI>://WOS:A1996UM90900008
Short TitleIsotropic second-order dipolar shifts in the rotating frame
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