Intersystem crossing cyclic ketones

Lee and coworkers (17) have also investigated the solution-phase photochemistry of cyclobutanone and have found (X - 310 nm) to be l/20th of that obtained in the vapor phase. This reduction has been attributed to enhanced predissociation by the interaction of vibrationally excited with neighboring solvent molecules. If this solvent interaction in addition to ring strain already present in the cyclic ketone both facilitate a-cleavage from the vibrationally excited state, relative to intersystem crossing to T, then it is not unreasonable to propose the cyclobutanone state as the precursor to some, if not all, of the observed photoproducts. 

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