He atomic beam scattering study of Pt(111) super-structure surface inducedby high energy molecular beam of H2O

The super-structure, Pt(111)-(2x2), is investigated both by He atomic beam scattering (HAS) and low energy electron diffraction. The structure is prod uced by irradiation of a high energy H2O molecular beam, which is accelerat ed up to about 300 meV hy dilution in He gas molecules. The HAS result show s that the structure is stable at 200 K and becomes unstable as the sample temperature is raised to 300 K. The observed structure is believed to be du e to reconstruction of the Pt(111) surface, which is caused by H atoms prod uced during the collision process of H2O molecules with sufficiently high e nergy for dissociation.