AVS 50th International Symposium
    Surface Science Friday Sessions
       Session SS1-FrM

Paper SS1-FrM4
HREELS Measurements of Iodine Vibrations on Cu(111) and Cu(221)

Friday, November 7, 2003, 9:20 am, Room 327

Session: Catalysis IV: Reactivity of Complex Systems
Presenter: D. Sung, Carnegie Mellon University
Authors: D. Sung, Carnegie Mellon University
A.J. Gellman, Carnegie Mellon University
Correspondent: Click to Email
Density functional theory calculations have shown that iodone atoms adsorb at the tops of the step edges on stepped Cu single crystal surfaces. In order to try to corroborate this prediction, we have measured and compared vibrational frequencies of iodine atoms adsorbed on the flat Cu(111) surface and the stepped Cu(221) surface using High Resolution Electron Energy Loss Spectroscopy (HREELS). Energy losses at 136 cm@super -1@ and 235 cm@super -1@ are observed on both surfaces. We assign these two frequencies to in-plane and out-of-plane vibrations of iodine on the (111) terrace sites. On a stepped surface one would expect the in-plane mode perpendicular to the step edge to be higher in frequency than the in-plane mode on the Cu(111) surface, if the atom is adsorbed at the bottom of the step edge. It would be expected to appear at a lower frequency if the atom is adsorbed at the top of the step edge. On the Cu(221) surface, an additional peak appears at 80 cm@super -1@, corresponding to the vibration of iodine adsorbed on the step edges of Cu(221). The fact that this new mode is at a lower frequency than the in-plane mode on the Cu(111) surface is consistent with the expectation that the iodine atom is adsorbed at the top of the step edge. The experimental results are consistent with the theoretical prediction that iodine atoms adsorb at the top of the step edges on the Cu(221) surface.