The Chemistry of Alkyl Iodides on Copper Surfaces. 1. Adsorption Geometry

Abstract

The adsorption geometries of iodomethane, iodoethane, 1-iodopropane, 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.

Titration of chiral kink sites on Cu(643) using iodine adsorption

“…Experimental work by Jenks et al [12,13] reported desorption of CuI and Cu sublimation. This and a TPD study [27] reported peak desorption temperatures of 900-950 K, corresponding to an energy barrier of $2.5 eV assuming a first-order desorption process.…”

“…This is followed by b-hydride elimination of the ethyl groups and finally, desorption of ethylene at temperatures below 300 K [12,13]. Since atomic I is stable on Cu surfaces up to temperatures of roughly 900 K, this process leaves atomic I on the surface.…”

“…The adsorption of atomic iodine on Cu(1 1 1) and Cu(1 0 0) has been studied in a number of previous experiments [7][8][9][10][11][12][13][14]. We discuss the details of these previous studies below by comparing the results of our DFT calculations with the experimental observations.…”

Density functional theory study of β-hydride elimination of ethyl on flat and stepped Cu surfaces

“…Jenks et al used temperature programed desorption ͑TPD͒ to characterize the thermal chemistry of iodoethane on different Cu surfaces. 6 This observation is somewhat surprising when compared to the usual expectation that the presence of surface step edges will enhance the reactivity of a surface. Sung and Gellman have measured the kinetics of ␤-hydride elimination reaction of ethyl on Cu͑111͒ and Cu͑221͒, 10 which has a ͑111͒ terrace separated by ͑110͒ steps, by depositing ethyl iodide on these surfaces.…”

“…6 ␤-hydride elimination was found to be the rate-limiting step, and this reaction was significantly faster on Cu͑110͒ than on either Cu͑100͒ or Cu͑111͒. Jenks et al used temperature programed desorption ͑TPD͒ to characterize the thermal chemistry of iodoethane on different Cu surfaces.…”