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Unexpected effects of third-order cross-terms in heteronuclear spin systems under simultaneous radio-frequency irradiation and magic-angle spinning NMR.

Tatton, A.S. and Frantsuzov, I. and Brown, S.P. and Hodgkinson, P. (2012) 'Unexpected effects of third-order cross-terms in heteronuclear spin systems under simultaneous radio-frequency irradiation and magic-angle spinning NMR.', Journal of chemical physics., 136 (8). 084503.

Abstract

We recently noted [R. K. Harris, P. Hodgkinson, V. Zorin, J.-N. Dumez, B. Elena, L. Emsley, E. Salager, and R. Stein, Magn. Reson. Chem. 48, S103 (2010)10.1002/mrc.2636] anomalous shifts in apparent 1H chemical shifts in experiments using 1H homonuclear decoupling sequences to acquire high-resolution 1H NMR spectra for organic solids under magic-angle spinning (MAS). Analogous effects were also observed in numerical simulations of model 13C,1H spin systems under homonuclear decoupling and involving large 13C,1H dipolar couplings. While the heteronuclear coupling is generally assumed to be efficiently suppressed by sample spinning at the magic angle, we show that under conditions typically used in solid-state NMR, there is a significant third-order cross-term from this coupling under the conditions of simultaneous MAS and homonuclear decoupling for spins directly bonded to 1H. This term, which is of the order of 100 Hz under typical conditions, explains the anomalous behaviour observed on both 1H and 13C spins, including the fast dephasing observed in 13C{1H} heteronuclear spin-echo experiments under 1H homonuclear decoupling. Strategies for minimising the impact of this effect are also discussed.

Item Type:Article
Full text:PDF - Published Version (595Kb)
Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1063/1.3684879
Publisher statement:© 2012 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Tatton, A.S. and Frantsuzov, I. and Brown, S.P. and Hodgkinson, P. (2012) 'Unexpected effects of third-order cross-terms in heteronuclear spin systems under simultaneous radio-frequency irradiation and magic-angle spinning NMR.', Journal of chemical physics., 136 (8). 08450
Record Created:12 Sep 2012 10:35
Last Modified:10 Jan 2013 16:34

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