O2 photodesorption from a Ag8O2- cluster

The decay path of an Ag 8 (O 2 ) - cluster photoexcited by a 3.1 eV photon is elucidated using time-resolved photoelectron spectroscopy. Photoabsorption results in the formation of an excited state giving rise to a peak in the photoelectron spectra with well-resolved vibrational finestructure. With a lifetime of about 100 fs this bound state decays into an anti-bonding state which dissociates into O 2 and Ag 8 - on a timescale of 10 ps. In the photoelectron spectra, this corresponds to a broad maximum shifting gradually towards higher binding energy while the O 2 and Ag 8 - separate. Finally, the spectrum of bare Ag 8 - appears. This process is unique to small clusters, because on metal surfaces excited state lifetimes are too short to allow for direct dissociation.