The excited-state structure and photophysics of isolated acenaphthylene

Abstract We report a picosecond time-resolved photoionization and photoelectron spectroscopic study of acenaphthylene, C 12 H 8 in a free jet. The origin for the A 1 B 2 (S 1 ) ← X 1 A 1 (S 0 ) transition is found at 21,757 ± 15 cm −1 , while the one for the B 2 A 1  ← X 1 A 1 transition is observed at 30,076 ± 27 cm −1 . For both transitions vibrational bands are resolved and assigned. For the origin of the S 1 state a lifetime of 380 ps is measured, which decreases with excess energy. Internal conversion to the electronic ground state seems to be the dominant deactivation pathway. For the S 2 state an additional component with a very short lifetime of 1 ps or less is observed. This indicates a two-step deactivation via S 1 to the electronic ground state. A small and unstructured signal in the photoelectron spectra at long delay times suggests the presence of an additional deactivation channel, most likely intersystem crossing.