Ultrafast Relaxation Dynamics of the S1 (nπ*) State and the 3p and 3d Rydberg States in Cyclohexanone by Femtosecond Photoelectron Imaging

The radiationless decay dynamics of the S1 (nπ*) state and the 3p and 3d Rydberg states of cyclohexanone are investigated using femtosecond time-resolved time-of- flight mass spectrometry and photoelectron imaging spectroscopy. After two-photon excitation of the 3p and 3d states, an ultrafast population transfer to the 3s state is observed within < 120 fs. We ascribe this behavior to strong vibronic interactions of the excited Rydberg states with the ¹ππ* valence state that enable an ultrafast population transfer via an avoided crossing and the subsequent passage of a conical intersection between the respective electronic states. Eventually, the 3s state deactivates by internal conversion to the S₁ (nπ*) state, which in turn is found to be long-lived with a decay time of ~ 300 - 800 ps.