The formation of metal–oxygen species at low temperatures

The interaction of solid molecular oxygen Li, Cs, K, La, Ag, Cu, and Ba has been studied at 35 K or below using photoemission. A feature near 535 eV in the O ls core level spectra was observed when Li, Cs, K and La were deposited on solid oxygen. This feature was identified with one electron being donated to an oxygen molecule, i.e., the superoxide species, which as far as we know has not been previously reported for La and Li. A feature at about 531.5 to 533 eV was identified as a peroxide species where two electrons were donated to an oxygen molecule. Finally features at about 528 to 530.5 eV were identified as oxide phases where the molecular oxygen was dissociated into atomic oxygen with formal valence of {minus}2. These identifications are crucial in the determinations of the exotic features in the XPS O ls spectra of the high T{sub c} superconductors. 13 refs., 4 figs.