In the present work, the potential energy profiles, governing the dissociation of cyclopropanone to CO＋C₂H₄ in the S₀, S₁ and T₁ states, have been determined using complete active space self-consistent field (CASSCF), density functional theory (DFT), and the second-order Moller-Plesset perturbation theory (MP2) in conjugation with the correlation-consistent atomic natural orbital basis set, cc-pVDZ. Upon photoexcitation in the range of 292～365 nm, the initial process was determined to be the α C—C bond cleavage after the cyclopropanone was excited to the S₁ state. Our research found that the S₁/S₀ intersection point played an important role in the subsequent processes. On one hand, the singlet diradical is produced as an intermediate, which is followed by formation of CO and CH₂＝CH₂ in the S₀ state. On the other hand, the “hot” parent molecule can be formed through the S₁/S₀ intersection point, which has enough internal energies to overcome the barrier on the pathway to CO and CH₂＝CH₂. Besides, the isomerization reactions of cyclopropanone in the ground state were investigated in this work.

Key words: cyclopropanone, ab initio calculation, photodissociation, isomerization, conical intersection