AVS 46th International Symposium
    Surface Science Division Monday Sessions
       Session SS2-MoM

Paper SS2-MoM11
Interaction of Atomic Hydrogen and Deuterium with the Ir(111)-p(1x1)-H, Ir(111)-p(1x1)-D, and Ir(111)-p(1x2)-O Surfaces

Monday, October 25, 1999, 11:40 am, Room 607

Session: Catalysis on Metals
Presenter: C.J. Hagedorn, University of California, Santa Barbara
Authors: C.J. Hagedorn, University of California, Santa Barbara
M.J. Weiss, University of California, Santa Barbara
W.H. Weinberg, University of California, Santa Barbara
Correspondent: Click to Email
The interaction of gas phase atomic hydrogen and deuterium with chemically modified Ir(111)-p(1x1)-D, Ir(111)-p(1x1)-H, and Ir(111)-p(1x2)-O surfaces at cryogenic temperatures has been studied using thermal desorption mass spectrometry and high-resolution electron energy loss spectroscopy. Although the Ir(111)-p(1x2)-O surface at a temperature of 90 K is passivated with respect to exposure to gas phase H@sub 2@ and D@sub 2@, the interaction of gas phase atomic H and D with this surface at 90 K results in the subsequent desorption of water in thermal desorption spectra. These results suggest that the dissociative chemisorption of molecular hydrogen on Ir(111) is precluded by the presence of the (1x2)-O oxygen overlayer, whereas energetically "hot" gas phase atomic hydrogen reacts readily with this oxygen modified surface. Moreover, a strong isotope effect has been observed in the interaction of gas phase atomic H and D with deuterium and hydrogen modified surfaces. The abstraction cross section for atomic D interacting with the Ir(111)-p(1x1)-H surface to form HD is approximately a factor of two greater than that for atomic H interacting with the Ir(111)-p(1x1)-D surface. This difference between the abstraction cross sections can be explained qualitatively by considering the differences associated with the expected zero point energy of the transition state for the abstraction reaction and the differences associated with the zero point energy between H and D adatoms.