| 1. |
- Antzutkin, Oleg, et al.
(author)
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Molecular motion of the Morpholin-1-yl radical in CF2 ClCFCl2 as studied by ESR : use of residual anisotrophy of powder spectra to extract dynamics
- 1993
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In: Chemical Physics. - 0301-0104 .- 1873-4421. ; 169:2, s. 195-205
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Journal article (peer-reviewed)abstract
- The dynamics of the deprotonated neutral morpholin-1-yl radical, trapped in a halocarbon matrix, CF2ClCFCl2, has been studied utilizing electron spin resonance (ESR) spectroscopy. The experimental lineshapes of the radical exhibit an alterating line-width effect in the temperature range 105-144 K. The major changes of the ESR lineshape were governed by the averaging of the nitrogen hyperfine anisotropy while no exchange of the isotropic hyperfine coupling constants was observed. Geometrical parameters specifying the restricted anisotropic rotation of the whole radical trapped in the matrix could be extracted. Two methods for simulating anisotropic exchange broadened ESR spectra, the secular and non-perturbative, were utilized to investigate the dynamics of the radical. A surprisingly simple ''three-site'' jump model with a barrier of almost-equal-to 3.6 kcal/mol can be applied in the simulation of the experimental spectra. It has been shown that the secular method cannot reproduce the exchange broadened ESR spectra of systems with large hyperfine anisotropy undergoing large internal reorganisation.
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| 2. |
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| 3. |
- Antzutkin, Oleg, et al.
(author)
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Optically dectected ESR (OD-ESR) of iron-radical pairs in colored solutions : observation of transient trans-Azobenzene radical cation
- 1993
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In: Applied Magnetic Resonance. - : Springer- Verlag. - 0937-9347 .- 1613-7507. ; 5:1, s. 77-86
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Journal article (peer-reviewed)abstract
- Trans-azobenzene dissolved in different liquid hydrocarbons absorbs fluorescence arising from all acceptors previously used in Fluorescence Detected Magnetic Resonance (FDMR) and Optically Detected ESR (OD ESR) spectroscopy making optical detection impossible. In this report a new acceptor, rubrene, having sufficient quantum yield of fluorescence in the red band 550-620 nm, has been proven successful. OD ESR spectra of the radical-ion pair trans-azobenzene+/rubrene- were detected in liquid squalane (2,6,10,15,19,23-hexamethyl-tetracosane) solution in the temperature range 294-243 K. The experimental isotropic hyperfine splittings of the radical cation of trans-azobenzene (a(N) = 1.4 mT) have been compared with those from MNDO/INDO calculations and with those of earlier work using freon matrix studies.
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| 4. |
- Antzutkin, Oleg, et al.
(author)
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Suppression of sidebands in magic-angle-spinning nuclear magnetic resonance : general principles and analytical solutions
- 1994
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 100:1, s. 130-140
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Journal article (peer-reviewed)abstract
- Several theoretical and experimental aspects of sideband suppression in the nuclear magnetic resonance (NMR) spectra of rotating solids are considered. The principles of sideband suppression are explored using general symmetry arguments and previous treatments are examined critically. Analytical solutions are given for sideband suppression pulse sequences employing four, five, six, and nine pulses. The analytical solutions for four pulses are complete. Experimental demonstrations are given. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.
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| 5. |
- Lindgren, M., et al.
(author)
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The [2H8]THF radical cation in CF3CCl3 and CFCl3 : an EPR and ENDOR study
- 1993
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In: Journal of the Chemical Society. Perkin Transactions 2 (2001). - 1472-779X .- 1364-5471. ; :11, s. 2009-2014
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Journal article (peer-reviewed)abstract
- The structure and dynamics of the radical cation of deuteriated tetrahydrofuran ([H-2(8)]THF) stabilized in the freon matrices CFCl3 and CF3CCl3 have been investigated by means of EPR and ENDOR spectroscopy. The EPR and ENDOR results of the rigid structure give two pairs of strongly interacting beta-deuterium hf splittings [a(D) = 1.36 (2 D) and a(D)) = 0.60 mT (2 D)] consistent with the protonated analogue [Kubodera et al., J. Phys. Chem., 1 981, 85, 2583 (ref. 1)]. An additional hf splitting (0.9-1.1 mT) assigned to the matrix fluorine was resolved above ca. 110 K in CFCl3. The temperature dependent EPR lineshapes (77-145 K) involving the exchange between four coupled (l = 1) nuclei have been analysed. A two-site model explained qualitatively the alterating line-widths at intermediate temperatures and resulted in an activation energy of ca. 1.7 kcal mol-1 A non-perturbative approach adopting a four-site model to account for puckering motion was tested. The dynamics were also manifested as a reversible temperature effect for the ENDOR. The relative abundance of resonances due to an averaged (hf) structure become predominant as the temperature is increased.
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| 6. |
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| 7. |
- Song, Zhiyan, et al.
(author)
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Sideband suppression in magic-angle-spinning NMR by a sequence of 5 π pulses
- 1993
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In: Solid State Nuclear Magnetic Resonance. - 0926-2040 .- 1527-3326. ; 2:3, s. 143-146
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Journal article (peer-reviewed)abstract
- We report a symmetrical sequence of 5 π pulses for total sideband suppression in magic-angle-spinning NMR. The sequence is almost evenly spaced and shorter than previous 4 and 6 π pulse methods.
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| 8. |
- Koptioug, Andrei, 1956-, et al.
(author)
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Effect of External Magnetic Fields and Resonance Radio frequency Radiation on Radical Reactions
- 1990
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In: Physica. B, Condensed matter. - : Esevier. - 0921-4526 .- 1873-2135. ; 164:1-2, s. 200-204
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Journal article (peer-reviewed)abstract
- It is well known that an external magnetic field can affect the rate of singlet-triplet transitions in a radical pair and hence its recombination probability in liquid. Resonance radiofrequency (RF) radiation induces quantum beats in the kinetics of radical pair recombination. At high RF field amplitudes the singlet-triplet transitions in radical pairs can be efficiently suppressed.
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| 9. |
- Morozov, V. A., et al.
(author)
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Multiquantum resonances in low-field optically detected ESR of radical-ion pairs
- 1991
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In: Molecular Physics. - : Taylor & Francis. - 0026-8976 .- 1362-3028. ; 73:3, s. 517-540
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Journal article (peer-reviewed)abstract
- Multiquantum resonances in low-field optically-detected electron spin resonance (ESR) spectra of radiation-induced radical-ion pairs of aromatic acceptors in liquid and some polymeric solutions have been studied experimentally and theoretically. Corresponding resonances occur in spectra under the action of relatively intense radiofrequency (RF) pumping, when usual signals are inverse due to spin-locking effect. Special experiments have been carried out to prove that such resonances are not caused by the apparatus. The dependencies of resonance shifts and intensities on the radiofrequency field amplitude for various polarizations of the RF field have been studied. The case of pumping with two independent RF generators has also been analysed. A general theory for multiquarium optically detected ESR spectra of radicalion pairs in liquid solutions has been developed, with spin relaxation processes being neglected. The theory has been applied to calculating multiquantum resonance parameters in transverse RF fields (H1 ⊥ H0) of various polarizations. The mechanism of multiquantum resonance spin dynamics of radical pairs (RP) has been analysed in detail. The shapes of OD ESR spectra components have been studied for the Poisson distribution of RP lifetimes. The developed theory shows qualitative agreement with experimental results
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