Composite structure of the stimulated nuclear polarization detected electron paramagnetic resonance spectra of the spin-correlated radical pairs in high magnetic fields

A Manifestation of two-quantum transitions in the ODEPR spectra of the spin-correlated radical pairs in micelles

“…12 the width of these narrow lines does not depend on (or is practically independent of) the amplitude of the alternating magnetic field. This statement contradicts the results of the previous theoretical calculations [8,9]. Therefore, we have comprehensively studied the shape and the width of these narrow lines with respect to the thermal mobility of radicals and other molecular-kinetic parameters, chemical reactivity of radicals, magneticresonance parameters of RPs.…”

“…(1). Such suppression of the S-T transitions is seen in the indirectly detected EPR spectra of the spin-correlated RPs as "narrow lines" [8,9]. At first glance it would seem rather straightforward to interpret these narrow lines in ODEPR or SNP-detected EPR spectra of the spin-correlated RPs as the two-quantum transition lines.…”

“…Indeed, in the conventional EPR spectra the two-quantum transition lines appear only for coupled spins in the pair, i.e., the two-quantum transition lines do not appear in the conventional EPR spectra of the RPs if the spin-spin interaction between the pair partners is negligible. As far as these narrow lines in the indirectly detected EPR spectra are concerned, they appear even when there is no interaction between the partners in the pair [8,9]. For this reason, the narrow lines expected in the ODEPR and other indirectly detected EPR spectra of the spin-correlated RPs (e.g., SNP-detected EPR, radiation-yield-detected magnetic resonance [RYDMR] [10]) are not associated with the two-quantum transitions in refs.…”

“…8 and 9. The following interpretation has been suggested to explain the narrow lines in the indirectly detected EPR spectra of the spin-correlated RPs [8,9]. The appearance of the narrow lines has been attributed to a suppression of the S-T transitions in the RPs due to a crossing of two energy levels or due to an avoided level crossing.…”

“…This paper is aimed at the development of a further theoretical consideration of the narrow lines in the EPR spectra of the spin-correlated RPs detected indirectly, like ODEPR spectra. In the previous treatments the narrow lines for ODEPR [8] and SNP-detected EPR [9] spectra were studied for the so-called exponential model of the RPs [1]. It was assumed that RPs can be found either in one or in two positions with fixed values of the exchange integral and the dipole-dipole interaction.…”