Bonding of molecular solids probed by low-energy H+ scattering. Water and oxygen on Pt(111)

Low-energy H+ ions are scattered from condensed O-2 and H2O layers formed o n the Pt(111) surface in order to investigate the nature of bonding of mole cular solids on the basis of the neutralization of H+. The H+ yield from th e H2O layer is found to be less than 1/60 of that from the O-2 layer. This is because the Is hole of H+ tends to be localized in the physisorbed O-2 m olecule, whereas the valence hole is rather delocalized in solid H2O due to hydrogen bonds with a considerable covalent character.