Probability of absorption/implantation of low-energy H₂⁺ ions in O-covered vanadium

Energy dependence of the absorption/implantation probability, α_ab, of H₂⁺ ions in vanadium covered by an oxygen monolayer was studied in the range 0.5-300 eV by plasma-membrane techniques. In contrast to what one would expect in the case of a clean surface, α_ab was found: (1) to be appreciably smaller than 1 (α_ab ≈ 0.2) at the lowest energies, and (2) to monotonically increase with ion energy, with a particularly steep rise in the range 0.5 to ∼7 eV - just where α_ab is expected to sharply decrease at a clean surface.