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Revisiting the Van Vleck second moment for characterizing molecular motion in organic solids

Sturniolo, Simone; Wickins, Helen M.; Hodgkinson, Paul

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Authors

Simone Sturniolo

Helen Wickins helen.m.wickins@durham.ac.uk
PGR Student Doctor of Philosophy



Abstract

Van Vleck’s classic theory of the second moment of lineshapes in 1H nuclear magnetic resonance (NMR) is reworked in a form that allows the effect of rapid molecular motion on second moments to be calculated in a semi-analytical fashion. This is much more efficient than existing approaches and also extends previous analyses of (non-dynamic) dipolar networks in terms of site-specific root-sum-square dipolar couplings. The non-local nature of the second moment means that it can discriminate between overall motions that are difficult to discriminate using alternative approaches, such as measurements of NMR relaxation. The value of reviving second moment studies is illustrated on the plastic solids diamantane and triamantane. In the case of triamantane, straightforward measurements of 1H lineshapes on milligram samples show that the molecules in the higher temperature phase undergo multi-axis jumps, information that is not accessible either to diffraction studies or to alternative NMR approaches. The efficiency of the computational methods means that the second moments can be calculated using a readily extensible and open-source Python code.

Citation

Sturniolo, S., Wickins, H. M., & Hodgkinson, P. (2023). Revisiting the Van Vleck second moment for characterizing molecular motion in organic solids. The Journal of Chemical Physics, 158(24), https://doi.org/10.1063/5.0151022

Journal Article Type Article
Acceptance Date Jun 7, 2023
Online Publication Date Jun 26, 2023
Publication Date Jun 28, 2023
Deposit Date Aug 17, 2023
Publicly Available Date Aug 17, 2023
Journal The Journal of Chemical Physics
Print ISSN 0021-9606
Electronic ISSN 1089-7690
Publisher American Institute of Physics
Peer Reviewed Peer Reviewed
Volume 158
Issue 24
DOI https://doi.org/10.1063/5.0151022
Keywords Physical and Theoretical Chemistry; General Physics and Astronomy
Public URL https://durham-repository.worktribe.com/output/1720523

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