Manifestations in the EPR spectrum shape of memory effects in the electron spin polarization in the case of two consecutive radical pairs

Abstract

Electron paramagnetic resonance (EPR) spectra of two consecutive radical pairs (RPs) diffusing inside micelles are numerically calculated. Calculations are carried out for various values of the micelle radius, exchange integral, and mutual diffusion coefficient. In the simple case when the hyperfine interaction with magnetic nuclei can be neglected, it is demonstrated that the spin dynamics in the primary radical pair (RP1) manifests itself in the EPR spectrum of the secondary radical pair (RP2) in a characteristic way: the oddness of the EPR spectrum with respect to its center is violated, and the EPR line intensities and widths for the two partners in the RP2 differ. These features of the RP2 EPR spectrum shape are interpreted as follows: the spin dynamics in the RP1 produces a longitudinal spin polarization and a transverse spin polarization (i.e., spin coherence). Both polarizations are transferred from RP1 to RP2. This spin polarization transfer causes the above features of the RP2 EPR spectrum shape. It is shown that the RP2 EPR spectrum in a sequence of RPs cannot be simulated as a spectrum of a single RP. The features of the RP2 EPR spectrum shape may be, in principle, exploited to reveal the existence of the short-lived RP1.