The chemistry of alkyl iodides on copper surfaces. 1. Adsorption geometry

The adsorption geometries of iodomethane, iodoethane, 1-iodopropanel and 2-iodopropane on Cu(110) single-crystal surfaces were characterized by using reflection-absorption infrared spectroscopy. At 100 K adsorption is molecular in all cases, but with adsorption geometries that change with increasing coverages. All alkyl iodides adsorb with the C-I bond perpendicular to the surface at low coverages and tilted at saturation. The hydrocarbon chains in iodoethane, 1-iodopropane, and 2-iodopropane follow the expected behavior, namely, the first molecules chemisorb flat on the surface and those added above about half a monolayer adopt a vertical orientation. All the adsorbed alkyl iodides decompose by 140 K via the scission of their C-I bond and generate alkyl groups on the surface. Those surface alkyls also change configuration with coverage, aligning themselves at saturation in a fashion reminiscence of that seen in self-assembled monolayers.