The electron spin polarized (CIDEP) spectrum of the propan-2-olyl radical

It is demonstrated that the origin of the absorptive contribution observed in the spin polarized esr spectrum of the propan-2-olyl radical when it is created by flash-photolysis of propan-2-one (acetone) in a hydrogen-donating solvent is not the triplet mechanism of CIDEP, as previously assumed. It is shown to arise not in the photochemistry or photophysics of the parent molecule, but rather to be a property of the radical pair itself. Arguments are presented to demonstrate that its origins may lie in an unidentified novel polarization process, rather than the possible redistribution of level populations via very fast relaxation processes.