SPIN DYNAMICS AND EPR-SPECTRA OF CONSECUTIVE SPIN-CORRELATED RADICAL PAIRS - MODEL-CALCULATIONS

Time-resolved continuous wave EPR signals of two consecutive radical p airs are found in the linear response limit. Numerical simulations of the EPR observables visualize two characteristic features. First, ther e is a shift of a phase of quantum beats of the EPR line intensities o f the secondary pairs. This phase shift originates from a certain time delay in a formation of the secondary pairs (due to time spent by ele ctron spins in the primary radical pair state) and from the difference of the spin dynamics in the secondary and the primary pairs. This pha se shift might be detected even in the cases when the primary radical pair has the very short lifetime and, as a result, the EPR spectrum of the primary pair cannot be detected directly. Second, for two consecu tive radical pairs, there might be a pronounced non-equality of intens ities of EPR lines at the EPR resonance frequencies of the secondary p airs. Indeed, in a case of two consecutive pairs there is the addition al mechanism which induces the non-equality of the EPR line intensitie s: a polarization transfer from the primary to secondary pair and the change of a electron spin quantization axis when a primary radical pai r transforms to a secondary radical pair. A possibility to detect expe rimentally these features of the EPR signals when studying consecutive charge separated states in photosynthetic reaction centers is discuss ed briefly.