A Theoretical Study on the Photodissociation of Acetone: Insight into the Slow Intersystem Crossing and Exploration of Nonadiabatic Pathways to the Ground State

Structures of transition states (TSs) and minima on seam of crossing (MSXs) for potential energy surfaces (PESs) of acetone of the S-0, S-1 and T-1 states were explored. On the basis of the results, we propose a new mechanism, slow intersystem crossing from S-1 to T-1 without seam of crossing, followed by CH3 dissociation via a TS on T-1 this slow pathway will be overtaken by a more efficient S-1 pathway for higher energy. This is consistent with the observed long lifetime of the S-1 species. Moreover, four channels, including three new ones, were found to regenerate the ground state acetone from the S-1 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.