Co-adsorption of O2 and C2H4 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 Au2+. Both studied complexes, Au2O2(C2H4)+ and Au2O2(C2H4)2+, show distinct features of both intact O2 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 O2 activation and the rather weak interaction between O2 and C2H4 are also reflected in the calculated electronic structure of the co-adsorption complexes which shows only a small occupation of the empty anti-bonding O2 2π*2p orbital as well as the localization of most of the Kohn–Sham orbitals on O2 and C2H4, respectively, with only limited mixing between O2 and C2H4 orbitals. The results are compared with theoretical studies on neutral AuxO2(C2H4) (x = 3, 5, 7, 9) complexes.
KeywordsGold cluster Ethylene oxidation Vibrational spectroscopy Density functional theory calculations Gas phase reaction
We gratefully acknowledge the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) for the support of the FELIX Laboratory. The research leading to these results has received funding from LASERLAB-EUROPE (grant agreement no. 654148, European Union’s Horizon 2020 research and innovation programme). Computations were carried out at the Georgia Tech Center for Computational Materials Science, and B.Y. and U.L. were supported by the Air Force Office for Scientific Research (AFOSR) (grant number FA9550-15-1-0519). S.M.L. is grateful to the Alexander von Humboldt Foundation for a Feodor-Lynen Scholarship, which, together with the above AFOSR grant, supported S.M.L.’s 6-month stay at the Georgia Institute of Technology during the work on this study.
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