Identification of the cationic excited state of cyclopentanone via time-resolved Ion yield measurements

Highlights: • CPO cationic excited states were investigated using fs pump-probe method. • Different ions exhibit opposite behavior in the pump-probe transients. • One 400 nm photon resonance in cationic excited states was experimentally identified. • The excited state was assigned as the D₄(²A) cationic state with VTE of 2.95 eV. • Dissociation mechanism of the D₄ state was discussed. We report the experimental evidence of the one-photon resonance in the cationic excited state of cyclopentanone using the femtosecond time-resolved pump-probe method. The transients of the parent ion and the C₂H₄⁺ fragment exhibit constant depletion in the pump-probe delay time up to 7 ps, however, that of the C₄H₈⁺/C₃H₄O⁺ fragment presents formation behavior. By recording dependence of the ion yields as the probe laser intensity, we demonstrate one 400-nm photon resonance in the cationic excited state, which is assigned as the D₄(²A) cationic state based on the theoretical calculations. Possible dissociation mechanism of the D₄ state is also discussed.