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Electron spin relaxation by spin-rotation interaction in benzoyl and other acyl type radicals


Makarov, T N; Bagryanskaya, E G; Paul, H (2004). Electron spin relaxation by spin-rotation interaction in benzoyl and other acyl type radicals. Applied Magnetic Resonance, 26(1-2):197-211.

Abstract

In various studies of the spin dynamics in radical pairs, benzoyl-type radicals have been one of the two paramagnetic pair species. Their electron spin relaxation has been assumed to be slow enough to be neglected in the data analysis. This assumption is checked by measuring the electron spin relaxation in a sequence of three acyl radicals (benzoyl, 2,4,6-trimethylbenzoyl and hexahydrobenzoyl) by time-resolved electron paramagnetic resonance spectroscopy. In contrast to the assumed slow relaxation, rather short spin-lattice relaxation times (100-400 ns) are found for benzoyl and 2,4,6-trimethylbenzoyl radicals from the decay of the integral initial electron polarization to thermal equilibrium at different temperatures and viscosities. The relaxation is induced by a spin-rotation coupling arising from two different types of radical movements: overall rotation of the whole radical and hindered internal rotation of the CO group. The predominant second contribution depends on the barrier of the internal rotation. The obtained results are well explained in the frame of Bull's theory when using a modified rotational correlation time τ J . The size of the spin-rotation coupling due to the internal CO group rotation in benzoyl radicals is estimated to be |C α|=1510 MHz

Abstract

In various studies of the spin dynamics in radical pairs, benzoyl-type radicals have been one of the two paramagnetic pair species. Their electron spin relaxation has been assumed to be slow enough to be neglected in the data analysis. This assumption is checked by measuring the electron spin relaxation in a sequence of three acyl radicals (benzoyl, 2,4,6-trimethylbenzoyl and hexahydrobenzoyl) by time-resolved electron paramagnetic resonance spectroscopy. In contrast to the assumed slow relaxation, rather short spin-lattice relaxation times (100-400 ns) are found for benzoyl and 2,4,6-trimethylbenzoyl radicals from the decay of the integral initial electron polarization to thermal equilibrium at different temperatures and viscosities. The relaxation is induced by a spin-rotation coupling arising from two different types of radical movements: overall rotation of the whole radical and hindered internal rotation of the CO group. The predominant second contribution depends on the barrier of the internal rotation. The obtained results are well explained in the frame of Bull's theory when using a modified rotational correlation time τ J . The size of the spin-rotation coupling due to the internal CO group rotation in benzoyl radicals is estimated to be |C α|=1510 MHz

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Item Type:Journal Article, refereed, original work
Communities & Collections:National licences > 142-005
Dewey Decimal Classification:170 Ethics
610 Medicine & health
Scopus Subject Areas:Physical Sciences > Atomic and Molecular Physics, and Optics
Language:English
Date:1 March 2004
Deposited On:19 Oct 2018 12:37
Last Modified:15 Apr 2021 14:54
Publisher:Springer
ISSN:0937-9347
OA Status:Green
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1007/bf03166572

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