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

Zhang, Bo; Abu-Khumra, Sabah; Aibout, Abdellah; Horsewill, Anthony J.

Abstract

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.

Citation

Zhang, B., Abu-Khumra, S., Aibout, A., & Horsewill, A. J. (2017). Manipulating and probing the polarisation of a methyl tunnelling system by field-cycling NMR. Journal of Chemical Physics, 146(6), Article 064302. https://doi.org/10.1063/1.4975173

• Journal Article Type: Article
• Acceptance Date: Jan 17, 2017
• Publication Date: Feb 8, 2017
• Deposit Date: Mar 9, 2017
• Publicly Available Date: Mar 9, 2017
• Journal: Journal of Chemical Physics
• Print ISSN: 0021-9606
• Electronic ISSN: 1089-7690
• Publisher: American Institute of Physics
• Peer Reviewed: Peer Reviewed
• Volume: 146
• Issue: 6
• Article Number: 064302
• DOI: https://doi.org/10.1063/1.4975173
• Keywords: Methyl tunneling, Field-cycling NMR
• Public URL: https://nottingham-repository.worktribe.com/output/847109
• Publisher URL: http://aip.scitation.org/doi/10.1063/1.4975173
• 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 http://aip.scitation.org/doi/10.1063/1.4975173
• Contract Date: Mar 9, 2017