Photochemical Reaction Mechanism of Intramolecular H Transfer Reaction of H2C3O+⋅ Radical Cation

Abstract

AbstractThe photochemical reaction mechanism underlying the intramolecular H‐transfer of the H2C3O+⋅ radical cation to the H2CCCO+⋅ methylene ketene cation was elucidated using time‐dependent density functional theory and high‐level ab initio methods. Once the D1 state of H2C3O+⋅ is populated, the reaction proceeds to form an intermediate (IM) in the D1 state (IM4D1). The molecular structure of the conical intersection (CI) was optimized using a multiconfigurational ab initio method. The CI is readily accessible because it lies slightly above the IM4D1 in energy. In addition, the gradient difference vector of the CI is almost parallel to the intramolecular H‐transfer reaction coordinate. Once the vibration mode of IM4D1 which is parallel to the reaction coordinate is populated, the degeneracy of the CI is readily lifted and H2CCCO+⋅ was formed via a relaxation pathway in the D0 state. Our calculated results clearly describe the photochemical intramolecular H transfer reaction reported in a recent study.