Manipulating and probing the polarisation of a methyl tunnelling system by field-cycling NMR

Zhang, Bo, Abu-Khumra, Sabah, Aibout, Abdellah and Horsewill, Anthony J. (2017) Manipulating and probing the polarisation of a methyl tunnelling system by field-cycling NMR. Journal of Chemical Physics, 146 (6). 064302. ISSN 1089-7690

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In NMR the polarisation of the Zeeman system may be routinely probed and manipulated by applying resonant rf pulses. As with spin-½ nuclei, at low temperature the quantum tunnelling states of a methyl rotor are characterised by two energy levels and it is interesting to consider how these tunnelling states might be probed and manipulated in an analogous way to nuclear spins in NMR. In this paper experimental procedures based on magnetic field-cycling NMR are described where, by irradiating methyl tunnelling sidebands, the polarisations of the methyl tunnelling systems are measured and manipulated in a prescribed fashion. At the heart of the technique is a phenomenon that is closely analogous to dynamic nuclear polarisation and the solid effect where forbidden transitions mediate polarisation transfer between ¹H Zeeman and methyl tunnelling systems. Depending on the irradiated sideband, both positive and negative polarisations of the tunnelling system are achieved, the latter corresponding to population inversion and negative tunnelling temperatures. The transition mechanics are investigated through a series of experiments and a theoretical model is presented that provides good quantitative agreement.

Item Type: Article
Additional Information: This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in Journal of Chemical Physics 146, 064302 (2017) and may be found at
Keywords: Methyl tunneling, Field-cycling NMR
Schools/Departments: University of Nottingham, UK > Faculty of Science > School of Physics and Astronomy
Identification Number:
Depositing User: Horsewill, Professor Anthony
Date Deposited: 09 Mar 2017 10:40
Last Modified: 04 May 2020 18:35

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