Co-adsorption of O and CH on a Free Gold Dimer Probed via Infrared Photodissociation Spectroscopy.

Infrared multiple photon dissociation (IR-MPD) spectroscopy in conjunction with density functional theory (DFT) calculations has been employed to study the activation of molecular oxygen and ethylene co-adsorbed on a free gold dimer cation Au. Both studied complexes, AuO(CH) and AuO(CH), show distinct features of both intact O and ethylene co-adsorbed on the cluster. However, the ethylene C=C double bond is activated, increasing in length by up to 0.07 Å compared with the free molecule, and the red shift of the O-O vibration frequency increases with the number of adsorbed ethylene molecules, indicating a small but increasing activation of the O-O bond. The small O activation and the rather weak interaction between O and CH are also reflected in the calculated electronic structure of the co-adsorption complexes which shows only a small occupation of the empty anti-bonding O 2π orbital as well as the localization of most of the Kohn-Sham orbitals on O and CH, respectively, with only limited mixing between O and CH orbitals. The results are compared with theoretical studies on neutral AuO(CH) (x = 3, 5, 7, 9) complexes.