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

Abstract

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 proximal to the OH group, 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 the nature of the substituent on the other end of the molecule. In the case of acetylacetones, the C–C bond cleavage is governed by the local intramolecular vibrational redistribution along the complex reaction coordinate, which appears to be statistical for CF3 release and non-statistical for CH3 release; however, it remains non-statistical over the entire molecular framework.