Relaxation dynamics of optically excited states of Au-3(-) and Au-3(-)(H2O)(m) were studied via femtosecond time-resolved photoelectron spectroscopy (fsTRPES). Au-3(-) exhibits photo-dissociation into either (Au-2(-) + Au-1) or (Au-2 + Au-1(-)) with a time constant of 1.6 ns. One water molecule adsorbed on Au-3(-) opened new photo-induced dissociation channel with a much shorter time constant. More than one water molecule on Au-3(-) inhibited photo-dissociation, most likely as a result of facile dissipation of excess energy of optically excited states by nuclear motions of clusters. The photochemical pathway can be controlled by adjusting the number of water molecules interacting with the ionic species. (C) 2012 Elsevier B. V. All rights reserved.