A Theoretical Study on the Photodissociation of Acetone: Insight into the Slow Intersystem Crossing and Exploration of Nonadiabatic Pathways to the Ground State
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Abstract
Structures of transition states (TSs) and minima on seam of crossing (MSXs) for potential energy surfaces (PESs) of acetone of the S<sub>0</sub>, S<sub>1</sub>, and T<sub>1</sub> states were explored. On the basis of the results, we propose a new mechanism, slow intersystem crossing from S<sub>1</sub> to T<sub>1</sub> without seam of crossing, followed by CH<sub>3</sub> dissociation via a TS on T<sub>1</sub>; this slow pathway will be overtaken by a more efficient S<sub>1</sub> pathway for higher energy. This is consistent with the observed long lifetime of the S<sub>1</sub> species. Moreover, four channels, including three new ones, were found to regenerate the ground state acetone from the S<sub>1</sub> PES, and they all may be involved in the roaming channel that has been proposed recently as a new route of CO generation in a 230 nm photolysis. There are significant differences in MSX structures and energies between the present CASPT2 results and previous CASSCF results