Abstract

The Chemically Induced Dynamic Electron Spin Polarization (CIDEP) of transient free radicals, as well as reaction orders and radical lifetimes, were studied with the aim to investigate the pathways and elementary mechanisms of the generation and disappearance of radicals in different liquid solutions of maleic anhydride (MA). Most measurements were carried through in tetrahydrofuran and 1,4-dioxane. The time-resolved measurements were performed by means of a modified ERS 220 ESR spectrometer at light pulse lengths in the μs-region. The two electrically neutral radicals formed by proton or by solvent addition to MA disappear primarily by second order reactions and have mean lifetimes between 30 μs and 10 ms, depending on solvent nature, concentration and temperature. The experimental facts point to the coexistence of both the photo-triplet and the radical pair mechanism in these systems with the radical pair mechanism being the major contributor to the observed CIDEP.

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