We report the first scanning tunneling microscope (STM) investigation, combined with densityfunctional theory calculations, to resolve controversy regarding the bonding and structure of chlorineadsorbed on Au(111). STM experiments are carried out at 120 K to overcome instability caused by mobilespecies upon chlorine adsorption at room temperature. Chlorine adsorption initially lifts the herringbonereconstruction. At low coverages (<0.33 ML), chlorine binds to the top of Au(111)-(1 × 1) surface
andleads to formation of an overlayer with (
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structure at 0.33 ML. At higher coverages, packingchlorine into an overlayer structure is no longer favored. Gold atoms incorporate into a complex superlatticeof a Au-Cl surface compound.