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Author Ernst, M. ♦ Kolbert, A. C. ♦ Schmidt-Rohr, K. ♦ Pines, A.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword PHYSICS ♦ COUPLING CONSTANTS ♦ SHIFT PROCESSES ♦ ORIENTATION ♦ HAMILTONIANS ♦ CHEMICAL SHIFT ♦ LINE BROADENING ♦ SPECTRA ♦ METHYLENE RADICALS ♦ METHYL RADICALS ♦ DIPOLES ♦ ISOTROPY
Abstract 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{endash}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 {ital P}{sub 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, CH{sub 2}, and CH{sub 3} 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. {copyright} {ital 1996 American Institute of Physics.}
ISSN 00219606
Educational Use Research
Learning Resource Type Article
Publisher Date 1996-06-01
Publisher Department Lawrence Berkeley National Laboratory
Publisher Place United States
Journal Journal of Chemical Physics
Volume Number 104
Issue Number 21
Organization Lawrence Berkeley National Laboratory


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