Formation of d-holes in the initial stages of the oxidation of Ag(001)

We demonstrate that double ionisation of the Ag atoms, leading to the forma tion of d-holes, takes place in the initial oxidation stage of Ag(001). The complex formed by the Ag2+ ion, two oxygen adatoms and one oxygen atom in the octahedral interstitial gives rise to a dipole active electron energy l oss at 130 me V. Signature of the electronic origin of this loss is the inv erse isotope shift and the peculiar temperature dependence of the energy lo ss, which can be reproduced by a theoretical model.