New Information About Manifestations of Spin Exchange in the EPR Spectra of Solutions of Paramagnetic Particles Under Saturation Conditions

• Published in: Applied magnetic resonance 2021-08, Vol.52 (8), p.1063-1091
• Main Author: Salikhov, K. M.
• Format: Article
• Language: English
• Subjects: Algorithms; Atoms and Molecules in Strong Fields; Continuous radiation; Electrons; Field strength; Foreign exchange rates; Gareth Eaton: on the Occasion of His 80th birthday; Laser Matter Interaction; Line broadening; Line spectra; Magnetic resonance; Numerical analysis; Organic Chemistry; Original Paper; Physical Chemistry; Physics; Physics and Astronomy; Relaxation time; Solid State Physics; Spectra; Spectroscopy/Spectrometry; Spectrum analysis; Spin exchange; Spin-lattice relaxation; Straight lines
• ISSN: 0937-9347; 1613-7507
• DOI: 10.1007/s00723-021-01364-9

For a model system of spins with two frequencies, a detailed analysis of the spin exchange in the EPR spectrum under saturation conditions in dilute solutions of paramagnetic particles is performed. For an arbitrary power of the microwave field, explicit analytical formulas are obtained for the frequency and width of the spectral lines, and for the contribution of the dispersion to the observed lines in the region of relatively slow spin exchange. A formula is obtained for the integral intensity of the spectrum for an arbitrary microwave field strength and spin exchange rate. The analysis of the dependence of the width of the spectrum lines and the contribution of the dispersion to the spectrum on the spin coherence transfer rate and on the microwave field power revealed the "destructive interference” of these factors in terms of their manifestation in the EPR spectra. It is shown that in a wide range of spin exchange rates up to the collapse of the spectrum, the dependence of the line broadening on the spin exchange rate is given by a straight line, the slope of which does not depend on the power of the microwave field. Extrapolating this straight line to the zero spin exchange rate gives a value that depends on the microwave field strength and the relaxation times of the longitudinal and transverse magnetization. The results obtained can be used to find the magnetic resonance parameters of the spins, including the spin–lattice relaxation time, from the continuous wave EPR spectroscopy data with high accuracy.