Local dynamics control the C–CX3 (X = H and F) bond photodissociation in acetylacetones

The primary photodissociation events of acetylacetone and its fluorinated analogs reveal that the translational energy distribution profiles of the CH3 and CF3 radicals follow a barrier-impulsive model for the C–C bond cleavage. Analysis based on the one-dimensional potential energy surfaces in the T1 state as well as dynamics simulations using on-the-fly semi-empirical potentials suggest that the C–C bond cleavage with OH in syn orientation, in general, is accompanied by proton migration. Interestingly, the near identical fragment translational energy distribution profiles of CH3 radical release from acetylacetone and trifluoroacetylacetone, as well as CF3 radical release from trifluoroacetylacetone and hexafluoroacetylacetone, suggest that the dynamics of formation of CH3 / CF3 radicals in acetylacetones appears to be independent of nature of the substituent on the other end of the molecule and the behaviour is akin to “let not thy left hand know what thy right hand doeth.” In the case of acetylacetones the C–C bond cleavage is governed by the local intramolecular vibrational redistribution (IVR) is either statistical or non-statistical along the ‘complex’ reaction coordinate yielding CF3 and CH3 radicals, respectively, and remains non-statistical over the entire molecular framework.