Cooperative and competitive coadsorption of H2, O2, and N2 on Au(x)+ (x = 3, 5)

The reactions of the small gas-phase gold cluster cations Au(3)(+) and Au(5)(+) with N(2), H(2), and O(2) as well as mixtures thereof were investigated in an octopole ion trap under multicollision conditions. While gold cations are inert toward molecular oxygen, a distinct reaction time and temperature dependent reaction behavior was observed toward H(2) and N(2). Introducing mixtures of the reactive gases to the ion trap revealed both, competitive and cooperative coadsorption effects: (i) A competitive displacement reaction was detected for the coadsorption of H(2) and N(2) indicating the molecular adsorption of these molecules onto the gold clusters. The enthalpy of the displacement reaction determined from equilibrium mass spectra was found to be small (<10 kJ/mol). (ii) Preadsorption of N(2) enabled the cooperative coadsorption of O(2) under special experimental conditions (low temperature and very small amounts of N(2)). In this surprising cooperative reaction even Au(x)O(2y)(+) were formed via elimination of the initially activating nitrogen molecules, whereas such complexes were never detected in reactions of gold cluster cations with pure molecular oxygen.