Low-energy H+ ions are scattered from condensed O-2 and H2O layers formed on the Pt(111) surface in order to investigate the nature of bonding of molecular solids on the basis of the neutralization of H+. The H+ yield from the 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 molecule, whereas the valence hole is rather delocalized in solid H2O due to hydrogen bonds with a considerable covalent character.