A contribution to the theory of OD EPR of spin-correlated radical pairs

A composite structure of OD EPR spectra is predicted. The OD EPR spectra consist of a broad component which manifests many features similar to conventional CW EPR spectra and a narrow component which appears as a hole in the broad spectrum. The width of the narrow component is estimated. The contribution of singlet-triplet dephasing to the shape of the OD EPR spectra is discussed comprehensively. It is shown that changes of the OD EPR spectra with an increase in the rate of singlet-triplet dephasing can be interpreted in terms of a redistribution of the populations of mixed (singlet and triplet) states of radical pairs and of exchange of the coherences corresponding to the EPR transitions for radical pairs.