| Abstract
| - Cyclic voltammetry and in situ scanning tunneling microscopy (STM) were used to examine iodine andcarbon monoxide (CO) chemisorbed at well-defined Ir(111) electrodes. Immersing an ordered Ir(111) electrodein 0.1 mM KI at 0.2 V resulted in oxidative adsorption of a monolayer of iodine, arranging in a well-ordered(√7 × √7)R19.1° structure. Adsorption from 1 mM KI solutions produced a bilayer of iodine comprising alower (√7 × √7)R19.1° overlayer and a higher hexagonal layer. STM atomic resolution yielded detailedspatial structures of these iodine overlayers. Irreversible adsorption of CO from CO-saturated 0.1 M HClO4solutions at 0.2 V rendered a monolayer of CO with unique island configurations. Most CO islands have4-column arrangements, with each individual column containing 3, 4, 5, and 4 CO molecules. A (3√3 ×3√3)R30° structure was identified in a local area uniformly covered by identical CO islands. All of theprotrusions in the STM images exhibit comparable intensity, implicating similar surface binding configurationsof CO molecules. This result is consistent with the predominant terminal binding for CO at Ir(111), as indicatedby IR spectroscopy.
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