Structures of Nitrogen Oxides Attached to Anionic Gold Clusters Au4- Revealed by Infrared Multiple Photon Dissociation Spectroscopy.

The adsorption forms of NO and NO2 on anionic Au4- clusters were investigated by a combination of IR multiple photon dissociation (IRMPD) spectroscopy and density functional theory (DFT) calculations. For all three species investigated (Au4NO-, Au4N2O2-, and Au4NO2-), the spectra were found to be consistent with a Y-shaped Au4- cluster with triangular Au3 and one Au atom sticking out, on which NO and NO2 molecules adsorb molecularly. These species are considered as intermediates of the Au4--mediated disproportionation reaction of NO, Au4(NO)3- → Au4(NO2)(N2O)-. We discuss the reaction path on the basis of the found geometries and energies and conclude that the disproportionation reaction of NO can occur catalytically on the Au4- cluster.