Two-Dimensional Field-Step ELDOR. A Method for Characterizing the Motion of Spin Probes and Spin Labels in Glassy Solids
✍ Scribed by J.W. Saalmueller; H.W. Long; G.G. Maresch; H.W. Spiess
- Publisher
- Elsevier Science
- Year
- 1995
- Tongue
- English
- Weight
- 549 KB
- Volume
- 117
- Category
- Article
- ISSN
- 1064-1858
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✦ Synopsis
A practical route for obtaining two-dimensional electron doublephase and amplitude distortions in the spectra. However, resonance spectra of radicals in disordered solids is presented in two-dimensional time-domain correlation experiments have detail. It involves narrow-band pulse excitation during a magnetic been carried out in single crystals and liquids (4-6), which field step combined with echo detection after a mixing time. The make use of linear prediction methods to correct for these equipment and experimental procedures are described, and factors distortions while analyzing the data. The 2D field-step elecaffecting the performance of the field-jump coil, spectral resolutron double-resonance (2D-FS-ELDOR) experiment involvtion, and sensitivity are thoroughly discussed. Simulated spectra, ing narrow-band pulse excitation and detection in combinawhich take into account distributions of correlation times, show tion with rapid stepping of the magnetic field is the first to the spectral features that can be observed with this technique.
enable the measurement of complete 2D correlation spectra These simulations have been improved over previous work by of nitroxide spin probes and spin labels in disordered solids taking into account g-tensor fluctuations, which is the dominant with uniform excitation over the entire EPR spectrum and effect in determining the anisotropy of the electron spin-lattice the exclusion of phase distortions (7). This offers new applirelaxation. Data for nitroxide radicals in polycarbonate at 110 K are analyzed and an orientation averaged nuclear spin-lattice cations of EPR in materials science since the dynamic behavrelaxation time of 82 { 13 ms and an electron spin-lattice relaxior of additives in polymers is of great interest, especially ation time for radicals oriented along the z direction (slowest relaxin the glassy state, where low-molecular-weight molecules ation) of 23 { 4 ms are measured. Simulations show that this of the nitroxide type (8) are used as plasticizers or antioxirelaxation is caused by highly restricted liberational motion with dants in polymers (9). a distribution of correlation times having mean of 0.1 ms and a
Well below the glass transition temperature, in the verywidth of about 0.8 decades in combination with a very narrow slow-tumbling regime (10), the effect of molecular motion mode having a correlation time of 10 ps.