Asymmetry in three-site relaxation exchange NMR
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Published:2023-08-24
Issue:2
Volume:4
Page:217-229
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ISSN:2699-0016
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Container-title:Magnetic Resonance
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language:en
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Short-container-title:Magn. Reson.
Author:
Blümich BernhardORCID, Parziale Matthew, Augustine Matthew
Abstract
Abstract. The asymmetry of peak integrals in 2D relaxation maps of exchange between three
sites indicates circular flow between the relaxation sites. This disagrees
with the detailed balance according to which the exchange between any pair of
sites must be balanced in terms of thermodynamic equilibrium. Confined diffusion of
particles jumping randomly on a 2D checkerboard grid to any of their eight
neighbor positions and confined gas diffusion were modeled in Monte Carlo
simulations to explore the impact of topological constraints on particle
exchange between three pools. Both models produce density variations across
the pore and reveal that up to 1 % of the molecules move in circular paths
between the relaxation pools. This motion is driven by different features of
either algorithm. It is silent in terms of thermodynamic equilibrium, confirming that
multi-site exchange maps are symmetric in this case. The coherent flux is
argued to result from stochastic pore resonance related to diffusion
eigenmodes. If it can be driven experimentally by external time-varying
electric, magnetic, or ultrasonic fields, this may be a way to enhance
heterogeneous catalysis.
Publisher
Copernicus GmbH
Subject
Atomic and Molecular Physics, and Optics,Condensed Matter Physics,Analytical Chemistry
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