Probing Ultrafast Electronic and Nuclear Dynamics during Ring-Opening Reactions*

We report the results of a time-resolved photoelectron spectroscopy experiment performed using short-pulse and narrow-bandwidth extreme ultraviolet radiation provided by the seeded free-electron laser FERMI. We studied the UV-induced ring-opening and subsequent unimolecular dissociation of a heterocyclic ring molecule. Theoretical predictions suggest the existence of several ring-opened isomers with about 1-2 eV less binding energy as compared to the parent molecule. Our experiment probes the ultrafast electronic pathways leading to their creation.