Journal
SOLID STATE NUCLEAR MAGNETIC RESONANCE
Volume 35, Issue 3, Pages 139-146Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.ssnmr.2008.08.005
Keywords
Field-cycling NMR; Nuclear spin relaxation; Tunnelling methyl groups; Molecular tunnelling; Tunnel resonance; Sodium acetate; Sorbic acid
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Funding
- Royal Society (Paul Instrument Fund)
- EPSRC
- China Postgraduate Scholarship from the University of Nottingham
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H-1 nuclear spin-lattice relaxation has been investigated in sodium acetate trihydrate and sorbic acid using field-cycling NMR in the solid state. The relaxation is dominated by the reorientation of the methyl groups. Resonant features arising from coherent tunnelling are observed in both the magnetic field dependence of the spin lattice relaxation rate, T-1(-1)(B-z) and in the inverse temperature dependence, T-1(-1)(1/T). The two systems have different barrier heights and tunnelling frequencies, providing different perspectives on the tunnel resonance phenomena. The magnetic field dependence enables different spectral density components to be separately investigated and in the carboxylic acid, sorbic acid, concerted proton transfer in the hydrogen bonds is also identified at low field and low temperature. The methyl hindering barriers and the correlation times characterising the reorientational dynamics has been accurately determined in both materials. (c) 2008 Elsevier Inc. All rights reserved.
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