On the applicability of the average exchange model for electron spin polarization phenomena

The applicability of the average exchange model as a tool for describing electron spin polarization in micelles is investigated by comparison with analytical and numerical results. The analytical results are used for the interpretation of the various types of dependence, while the numerical results are used for quantitative tests. It is demonstrated that the dephasing effect of the exchange interaction has a significant influence both on the time dependence and on the stationary value of the polarization. Dephasing arising from the exchange interaction is not included in the average exchange model, and therefore the spin dynamics are not described correctly. The average exchange model can only be used to estimate the frequency and the stationary value of the polarization, and only in the case of very slow singlet-triplet mixing, weak exchange interaction, and low reactivity of the radicals.