Direct observation of molecularly-aligned molecules in the second physisorbed layer-CO/Ag(1 1 0)

We report the direct observation of oriented second-layer physisorbed molecules on a single crystal surface by electron stimulated desorption. Experiments and simulations show that the orientation of the second-layer physisorbed CO molecules on Ag(1 1 0) is the result of both electrostatic and dispersion forces from the underlying chemisorbed CO and Ag atoms. At 25 K, the physisorbed C–O bond is tilted and azimuthally oriented with the C–O bond axis inclined in an azimuthal plane at 45° to the principal Ag(1 1 0) azimuthal crystallographic directions. The O atom in CO is directed outward, giving an O+ beam at 43° to the normal.