Kinetic Model for Determination of Reaction and Polarization Dynamics from Chemically Induced Electron Spin Polarized Electron Spin Resonance Spectra

The dynamics of photochemical reactions exhibiting chemically induced electron spin polarization (CIDEP) are modeled by kinetic equations that include all relevant parameters, including reaction of the excited precursor as both a singlet and a triplet and spin exchange during radical encounters. Analysis of the acetone/2-propanol photolysis reveals spin exchange effects and provides further evidence that the anomalous net electron spin resonance (ESR) absorption of the 2-propanolyl radical is due to spin−lattice relaxation in the triplet acetone precursor. The weakening of this net absorption in acetone/triethylamine photolyses is due to the rapid reaction of photoexcited acetone with triethylamine resulting in reaction via both its singlet state, which cannot produce a net polarization, and its triplet state, which yields no triplet polarization and reacts before spin−lattice relaxation can produce full equilibrium polarization.