Preprints
https://doi.org/10.5194/mr-2024-21
https://doi.org/10.5194/mr-2024-21
19 Nov 2024
 | 19 Nov 2024
Status: this preprint is currently under review for the journal MR.

Pseudo Rotary Resonance Relaxation Dispersion Effects in Isotropic Samples

Evgeny Nimerovsky, Jonas Mehrens, and Loren B. Andreas

Abstract. Enhanced transverse relaxation near rotary-resonance conditions is a well-documented effect for anisotropic solid samples undergoing magic-angle spinning (MAS). It is a surprising behavior for rotating liquids, in which first-order anisotropic interactions are averaged at a much faster timescale as compared with the spinning frequency. Here we report measurements of 13C transverse relaxation under spin lock for spinning samples of both polybutadiene rubber and polyethylene glycol solution. Maxima in the relaxation rates are observed when the spin-lock frequency matches one or two times the MAS rate. Through simulations, we qualitatively describe the appearance of this effect, which can be explained by time dependence caused by sample rotation and an inhomogeneous rf-field distribution. Consideration of this effect is important for MAS experiments based on rotary-resonance conditions, and motivates the design of new MAS coils with improved rf-field homogeneity.

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Evgeny Nimerovsky, Jonas Mehrens, and Loren B. Andreas

Status: open (until 17 Dec 2024)

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Evgeny Nimerovsky, Jonas Mehrens, and Loren B. Andreas
Evgeny Nimerovsky, Jonas Mehrens, and Loren B. Andreas

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Short summary
Local dynamics in rotating solids can be investigated by measuring enhanced transverse relaxation rates near rotary resonance conditions. In contrast, this effect is not expected in rotating solutions, as first-order anisotropic interactions are averaged out. For rotating solutions, we show how enhanced transverse relaxation near rotary resonance reports on fluctuations that are introduced due to imperfect hardware, with rf-field imperfections being the primary source of the effect.