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Impact of molecular size on electron spin relaxation rates of nitroxyl radicals in glassy solvents between 100 and 300 K

Sato, Hiedo, Kathirvelu, Velavan, Fielding, Alistair, Blinco, James P., Micallef, Aaron, Bottle, Steven E., Eaton, Sandra S., & Eaton, Gareth R. (2007) Impact of molecular size on electron spin relaxation rates of nitroxyl radicals in glassy solvents between 100 and 300 K. Molecular Physics, 105(15-16), pp. 2137-2151.

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Abstract

Electron spin lattice relaxation rates were measured for 12 nitroxyls with molecular weights between 144 and 438, and for galvinoxyl, 1,3-bisdiphenylene-2-phenylallyl (BDPA), and 2,2-diphenyl-1-picrylhydrazyl (DPPH) in glassy sucrose octaacetate. Relaxation rates for polar nitroxyls also were measured in glassy sorbitol. Dependence on T where Veff is effective molecular volume and γ is a material-specific parameter, was used to compare processes. Values of Veff were determined based on molecular libration in glassy sucrose octaacetate (γ = 3.5), tumbling in viscous decalin at 233 K (γ = 4.7), or tumbling in heavy mineral oil (γ = 6.0). For nitroxyl relaxation there is a master curve: log(1/T1) vs log( T) (γ = 0.89). The similarity of the values of γ for the Raman process and for the additional process that contributes at higher temperatures, and the absence of frequency dependence between X- and Q-band, support assignment of this additional process as a local mode. For these radicals the contributions from the local mode and the Raman process are correlated and follow trends in spin-orbit coupling. The temperature dependence of spin echo dephasing in sucrose octaacetate is dominated by rotation of methyl groups and by a motional process analogous to the Raman process.

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ID Code: 15078
Item Type: Journal Article
Keywords: Nitroxyl radicals, Spin, lattice relaxation, Raman process, Local mode, Volume scaling of thermodynamic parameters
DOI: 10.1080/00268970701724966
ISSN: 1362-3028
Subjects: Australian and New Zealand Standard Research Classification > CHEMICAL SCIENCE (030000) > PHYSICAL CHEMISTRY (INCL. STRUCTURAL) (030600) > Chemical Thermodynamics and Energetics (030602)
Divisions: Past > QUT Faculties & Divisions > Faculty of Science and Technology
Copyright Owner: Copyright 2007 Taylor & Francis
Copyright Statement: This is an electronic version of an article published in [Molecular Physics 105(15/16):pp. 2137-2151]. [Molecular Physics] is available online at informaworldTM with http://dx.doi.org/10.1080/00268970701724966
Deposited On: 10 Oct 2008
Last Modified: 29 Feb 2012 23:37

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