Two chemisorbed species of O2 on Ag(110)

Using electron energy loss spectroscopy and thermal desorption spectroscopy, we show that the adsorption of O-2 on Ag(110) creates two distinct molecular chemisorbed species. Only one, alpha-O-2, can be accessed by warming (converting) the physisorbed state and, unlike beta-O-2, does not dissociate to atomic O at higher temperatures. With the aid of molecular dynamics simulations, we propose that the lateral interaction between neighboring O-2 molecules in a dense physisorbed layer stabilizes the appropriate precursor orientation to enable the conversion into alpha-O-2 to occur.