Ethyl iodide decomposition on the Cu(1 1 1) and Cu(2 2 1) surfaces has been studied using thermal desorption spectroscopy and high resolution electron energy loss spectroscopy. On both surfaces ethyl iodide decomposes to produce ethyl groups and adsorbed iodine atoms. The ethyl groups decompose by b-hydride elimination to desorb as ethylene leaving adsorbed iodine atoms. The kinetics of b-hydride elimination on the Cu(2 2 1) surface are similar to those on the Cu(1 1 0) surface suggesting that the ethyl groups are reacting at the (1 1 0) step edges rather than on the (1 1 1) terraces. Vibrational spectra of the iodine atoms remaining on the surfaces after decomposition of the ethyl groups have been used to probe the iodine binding sites and to corroborate predictions based on density functional theory that the iodine atoms bind to the tops of the step edges. Iodine atoms on Cu(1 1 1) exhibit vibrational modes at 130 and 235 cm À1 that we assign empirically to in-plane and out-of-plane vibrations, respectively, of iodine atoms adsorbed at fcc sites on the (1 1 1) plane. On the stepped Cu(2 2 1) surface an additional peak appears at 80 cm À1 arising from iodine adsorbed at the step edges. The fact that this mode is at a lower frequency than the in-plane mode on the Cu(1 1 1) surface suggests that the iodine atom is adsorbed at the top of the step edge where its motion is unconstrained. These experimental results are consistent with the theoretical prediction that iodine atoms adsorb at the top of the step edges on the Cu(2 2 1) surface.

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