mriselMagnetic Resonance in SolidsMagnetic Resonance in Solids2072-5981Kazan Federal University10.26907/mrsej-20101mrisel-31Research ArticleСтатьиRelaxation due to thermal vibrations in pulsed EPR: Cylindrical-fluctuation model of perturbation of g- and A-matrices of an electron-nuclear spin-coupled system in a malonic-acid single crystalMisraS. K.

Physics Department, 1455 de Maisonneuve Boulevard West, Montreal, Quebec H3G 1M8

sushil.misra@concordia.caSalahiH. R.

Physics Department, 1455 de Maisonneuve Boulevard West, Montreal, Quebec H3G 1M8

Concordia UniversityCanada20202201202022120101 (16 pp.)Copyright © Misra S.K., Salahi H.R., 20242024Misra S.K., Salahi H.R.Misra S.K., Salahi H.R.Данная работа распространяется под лицензией Creative Commons Attribution 4.0.This work is licensed under a Creative Commons Attribution 4.0 License.https://www.mrsej.ru/jour/article/view/31

In the context of pulsed electron paramagnetic resonance (EPR), the correlation time (τc) and an effective parameter, representing the fluctuation of the director of the malonic-acid molecule due to thermal motion in the directions transverse to the molecular symmetry axis, are calculated. These calculations are made using the experimental electronic and nuclear spin relaxation times of an electron-nuclear spin-coupled system (electron spin S=1/2; nuclear spin I=1/2), as determined from echo electron-electron double-resonance (echo-ELDOR) measurements in a γ-irradiated malonic acid single crystal for a specific orientation of the external magnetic field with respect to the crystal axes. To this end, thermal motion of the molecule is considered to cause fluctuations in the values of the g- and A (hyperfine) matrices of the spin system, which are calculated using the model of Frezzato et al. [J. Phys. Chem. B, 108, 9505 (2004)] as functions of the thermal motion of the malonic-acid molecule in the directions transverse to its symmetry-axis. These fluctuations, i.e. the time-dependent variation from the average values of the spin-Hamiltonian parameters, are then used to calculate the four electronic (T2e) and two nuclear (T2n) spin-relaxation times, which constitute six duplicates of diagonal elements of the relaxation matrix in Liouville space for the four-level coupled electron-nuclear spin system, as outlined by Lee et al. [J. Chem. Phys. 98, 3665-3689 (1993); hereafter LPF]. The four electronic- and two nuclear-spin relaxation times, are then found to be functions of τc, the correlation time, and a fluctuation-limiting factor, h, which, in turn, are estimated from the two experimentally known average values of the electronic and nuclear spin-relaxation times, (T2e)exp and (T2n)exp, respectively, determined from the spin-echo correlation spectroscopy (SECSY) and echo-ELDOR signals data [LPF]. A rather narrow region of such τc and h values is found, giving a theoretical estimate to the values at its center: τc=8.9 × 10-8s and h=0.11, which are then used to calculate the time-dependent echo-ELDOR signal by exploiting the relevant Liouville-von Neumann equation, whose Fourier transform is found to be in very good agreement with that obtained by the experiment.

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The authors declare that there are no conflicts of interest present.