Ethyl iodide decomposition on Cu(111) and Cu(221)

Abstract

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.

Bridging the structure gap: Chemistry of nanostructured surfaces at well-defined defects

“…The same effect was reported also for sputtered Ag(100) [257]. This confirms that extended (100) terraces are (410). Data are compared with previous results for Ag (100) and Ag (110).…”

“…as soon as desorption from the molecular well becomes important over the time scale of the experiment (0.3 s). The curves for Ag (410) and Ag (110) coincide up to 350 K, at which temperature S 0 (T ) becomes steeper for Ag (410). Such difference is due to the dissociation process, which occurs only at steps for Ag (410) and takes place at regular sites for Ag (110).…”

“…Data are compared with previous results for Ag (100) and Ag (110). In the inset, indicate data for Ag(100); the large enhancement of S 0 at E i = 0.09 eV for Ag (410) evidences the presence of a non-or-poorly activated adsorption channel related to the presence of steps. Panel (b): O 2 is dosed on Ag(410) normally (θ = 31 • , open circles) and grazing (θ = −30 • , filled circles) to the step rises and on Ag(210) nearly normal to the step rises (θ = 20 • , stars).…”

“…The former threshold, on the contrary, must correspond to the O 2 interaction with the step heights, since it is not present for LMI planes and on Ag (410) it is much less evident both at θ = 0 • and θ = −30 • .…”

“…The choice of such geometry was guided by the suggestion, gained in previous O 2 adsorption experiments on flat and sputtered Ag (100), that kinks are indeed the active sites for O 2 dissociation [256,257]. Moreover, Ag (410) is well known to be the stable, faceted phase of Ag(100) upon massive O 2 exposure [258], i.e. it is expected to be closer to the real surface structure under atmospheric conditions.…”