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<p>It is generally accepted that the resonant homogeneously broadened line of the EPR spectrum has a Lorentz shape. However, in the presence of the spin exchange process, this is not the case. The resonant line of the spectrum has a mixed shape. It can be represented as the sum of two Lorentzian curves: absorption and dispersion. This follows from the solution of kinetic equations for ensembles of magnetizations. These equations take into account the processes of coherence transfer and decoherence that arise in the presence of spin exchange and dipole–dipole interaction. From the concentration dependences of the absorption and dispersion contributions, one can obtain the rate constants due to the spin exchange and dipole–dipole interaction. In this work, we present decomposition of experimental spectra of nitroxide radical [15N]-4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl in toluene. From this decomposition, the values of the rate constants were found. All presented experimental spectra were obtained in the linear response conditions.</p>

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Mixed Shape of EPR Spectrum Lines Under Conditions of Slow Spin Exchange

  • 期刊论文

  • 发表日期：

    2025年8月8日

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  • I. T. Khairutdinov,
  • K. M. Salikhov,
  • M. M. Bakirov,
  • R. B. Zaripov

摘要

It is generally accepted that the resonant homogeneously broadened line of the EPR spectrum has a Lorentz shape. However, in the presence of the spin exchange process, this is not the case. The resonant line of the spectrum has a mixed shape. It can be represented as the sum of two Lorentzian curves: absorption and dispersion. This follows from the solution of kinetic equations for ensembles of magnetizations. These equations take into account the processes of coherence transfer and decoherence that arise in the presence of spin exchange and dipole–dipole interaction. From the concentration dependences of the absorption and dispersion contributions, one can obtain the rate constants due to the spin exchange and dipole–dipole interaction. In this work, we present decomposition of experimental spectra of nitroxide radical [15N]-4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl in toluene. From this decomposition, the values of the rate constants were found. All presented experimental spectra were obtained in the linear response conditions.