The Role of Active Crossings in the Development of MARY Signals in the Spin System of a Radical Pair

Abstract

We have analyzed the origin of the characteristic lines that occur on the curves of the stationary magnetic field effect in chemical reactions due to coherences in the spin system of radical pairs, and have explicitly linked them to the active crossings in the energy levels of the spin system, i.e., crossings of the levels that can be simultaneously populated from the same initial state and thus can interfere. The notion of active crossings is a reflection of the selection rules for electron-nuclear spin system of the radical pair, and helps develop intuitive understanding of the level-crossing spectra similar to building stick diagrams in the spectra of magnetic resonance. The essential properties of active crossings are demonstrated analytically on two simple, but adequate for the job, models.