Co‐Adsorption of O 2 and CO on Au 2 − : Infrared Photodissociation Spectroscopy and Theoretical Study of [Au 2 O 2 (CO) n ] − ( n =2–6)

The co‐adsorption of O 2 and CO on anionic sites of gold species is considered as a crucial step in the catalytic CO oxidation on gold catalysts. In this regard, the [Au 2 O 2 (CO) n ] − ( n =2–6) complexes were prepared by using a laser vaporization supersonic ion source and were studied by using infrared photodissociation spectroscopy in the gas phase. All the [Au 2 O 2 (CO) n ] − ( n =2–6) complexes were characterized to have a core structure involving one CO and one O 2 molecule co‐adsorbed on Au 2 − with the other CO molecules physically tagged around. The CO stretching frequency of the [Au 2 O 2 (CO)] − core ion is observed around ν ˜ =2032–2042 cm −1 , which is about 200 cm −1 higher than that in [Au 2 (CO) 2 ] − . This frequency difference and the analyses based on density functional calculations provide direct evidence for the synergy effect of the chemically adsorbed O 2 and CO. The low lying structures with carbonate group were not observed experimentally because of high formation barriers. The structures and the stability (i.e., the inertness in a sense) of the co‐adsorbed O 2 and CO on Au 2 − may have relevance to the elementary reaction steps on real gold catalysts.