ИСТИНА

EPR spectroscopy is one of the most informative methods for study the processes of diffusion. Influence of rotation of paramagnetic molecules on the width and shape of EPR lines is well known, the numerical analysis of spectra allows determining the rotational diffusion coefficient Drot of probe molecules even in case of anisotropic rotation [D.E.Budil, S.Lee, S.Saxena, J.H.Freed, J. Magn. Reson. Ser.A, 1996,120, 155-189.]. The effect of translational diffusion on the shape of EPR spectra is less studied, and the straight analysis of spectra for measurement the translational diffusion constant Dtr is more complicated. One of the possible approaches for determination of Dtr is the analysis of Heisenberg exchange of paramagnetic molecules which is reflected in concentrational broadening of EPR spectra lines. Because of high viscosity of ionic liquids the broadening of lines is caused not only Heisenberg exchange but also dipole-dipole interaction of radicals. Moreover, the ratio between these two kinds of interaction changes according to Dtr. At present work the contribution of Heisenberg exchange to concentrational broadening of EPR spectra lines was separated correspondingly the methodical approach suggested in [A. Nayeem, S.B. Rananavare, V.S.S. Sastry, J.H. Freed, J. Chem. Phys. 1989, 91(11), 6887-6905]. The temperature dependence of concentrational broadening divided by concentration of solution of radical TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl) in ionic liquid omimBF4 as well as contributions of exchange and dipole-dipole interactions are shown on the Figure. In this work we determined the effective activation energies for translation and rotation of TEMPOL in series of ionic liquids and in some low and high viscous molecular solvents.