The coadsorption of chlorine and oxygen on Ag(111): Detection of electrophilic oxygen in the ClO and ClO3 quasimolecules

The coadsorption of chlorine and oxygen on the Ag(111) surface has been studied with low-temperature scanning tunneling microscopy in combination with density functional theory (DFT) calculations. The coadsorption systems were created in two ways: either by the oxidation of the chlorinated Ag(111) surface or by chlorination of the oxidized sample. Depending on the stoichiometry, a series of new well-ordered coadsorbed structures containing both oxygen and chlorine atoms has been discovered. The DFT analysis has shown that all the structures correspond to the reconstruction of the silver (111) surface. Moreover, the reconstruction is formed by silver triangles with atoms occupying either fcc or hcp positions. Most chlorine and oxygen atoms occupy nearly fourfold positions similar to those in the p(4 × 4)-O and (3 × 3)-Cl reconstructions. A characteristic feature of all coadsorbed structures is the presence of bright objects, which we associate with ClO3 and ClO quasimolecules. Using DFT, we calculated the O 1s binding energies for all oxygen atoms in the structures. The binding energy of oxygen atoms in the nearly fourfold positions is 528 eV [as in the Ag(111)-p(4 × 4)-O phase], while the binding energies of oxygen atoms in ClO3 and ClO quasimolecules are 531 and 530 eV, respectively, indicating their electrophilic nature.