Non-perturbative treatment of the solid effect of dynamic nuclear polarization

  • In the solid effect of dynamic nuclear polarization (DNP), the concerted flips of the electronic and nuclear spins, which are needed for polarization transfer, are induced by the microwaves. Commonly, the effect of the microwaves is modeled by a rate process whose rate constant is determined perturbatively. According to quantum mechanics, however, the coherent microwave excitation leads to Rabi nutation, which corresponds to a rotation rather than a rate process. Here we reconcile the coherent effect of the microwaves with the description by rate equations by focusing only on the steady state of the spin dynamics. We show that the phenomenological rate constants describing the synchronous excitation of the electronic and nuclear spins can be selected such that the description by rate equations yields the same steady state as the exact quantum-mechanical treatment. The resulting non-perturbative rates differ from the classical, perturbative ones and remain valid also at the high microwave powers used in modern-day DNP. Our treatment of the solid effect highlights the role of the coherences in the mechanistic steps of polarization transfer and reveals the importance of the dispersive (i.e., out-of-phase) component of the EPR line. Interestingly, the multiplicative dependence of the DNP enhancement on the dispersive EPR component was intuited in the very first report of the solid effect in liquids (Erb et al., 1958a). The time-domain description of the solid effect developed here is extendable to liquids, where the dipolar interaction changes randomly in time due to molecular diffusion.

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Author:Deniz SezerORCiD
URN:urn:nbn:de:hebis:30:3-875431
DOI:https://doi.org/10.5194/mr-4-129-2023
ISSN:2699-0016
Parent Title (English):Magnetic resonance
Publisher:Copernicus Publications
Place of publication:Göttingen
Document Type:Article
Language:English
Date of Publication (online):2023/06/05
Date of first Publication:2023/06/05
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2024/10/29
Volume:4
Issue:1
Page Number:24
First Page:129
Last Page:152
Note:
Funding: DFG ; 405972957
Note:
Gefördert durch den Open-Access-Publikationsfonds der Goethe-Universität.
Note:
The code used to generate the figures is at https://github.com/dzsezer/solidDNPliquids (https://doi.org/10.5281/zenodo.7990757, Sezer, 2023b).
Institutes:Biochemie, Chemie und Pharmazie
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 53 Physik / 530 Physik
5 Naturwissenschaften und Mathematik / 54 Chemie / 540 Chemie und zugeordnete Wissenschaften
Sammlungen:Universitätspublikationen
Open-Access-Publikationsfonds:Biochemie, Chemie und Pharmazie
Licence (German):License LogoCreative Commons - CC BY - Namensnennung 4.0 International