The kinetics of the interaction of Ag-2(+) with O-2 is studied in the gas phase under multi-collision conditions at various temperatures. A new experimental scheme is employed, which consists of an octopole ion trap of variable temperature inserted into a tandem quadrupole mass spectrometer. From the time evolution of the reactant and product molecule concentrations at different temperatures the corresponding reaction mechanism is extracted. Surprisingly, the product Ag2O+ is detected, which is formed after molecular adsorption and dissociation of O-2, We can clearly identify Ag2O2+ as an intermediate in this reaction. In addition, absolute rate coefficients and activation energies for the molecular adsorption of O-2 onto Ag-2(+) are presented.