Ab initio studies for the photodissociation mechanism of hydroxyacetone

The reaction pathways for CH₃COCH₂OH (hydroxyacetone) photodissociation on the low-lying electronic states have been studied with use of the CASSCF energy gradient techniques. The S₀/S₁ and S₁/T₁ intersection points were determined by the state-average CASSCF method. Two main reaction pathways, which are possible to the photodissociation, have been studied. It has been found that the mechanism is stepwise, and belongs to Norrish type-I reaction. The n → π* excitation leads to the first excited singlet state, followed by the intersystem crossing from S₁ to T₁. On the T₁ potential energy surface, the system can dissociate adiabatically to CH₃(x̃)+COCH₂OH(x̃) and CH₃CO(x̃)+CH₂OH(x̃). The COCH₂OH(x̃) and CH₃CO(x̃) radicals can further dissociate into CO, OH, and other fragments. Our calculated results are in good agreement with recent experimental results.