Isotope effects in the interaction of hydrogen and deuterium with a rhodium (110) surface

Abstract

The adsorption of H₂ and D₂ on a Rh (110) surface at 100 K leads to a sequence of ordered phases, among others 1×2 phases atθ _H =0.5 and atθ _H =1.5 which likely involve a partial surface reconstruction consisting of a small perpendicular displacement of Rh surface atoms. The structure of the adsorbate phases is strongly correlated with the binding energy of the adsorbed phases. Three H (D) binding states (α₁,α₂ andβ) are populated at saturation as determined by thermal desorption spectroscopy (TDS). Whereas the peak temperature of theβ state is invariant with the hydrogen isotope, the D α₁ state appears at a ∼8 Klower and theD α₂ state at a ∼5 Khigher temperature than the respective H states. Generally the D phases exhibit a better long-range order than the H phases. The rate of adsorption is identical for the first three adsorbed phases but D₂ adsorbs appreciably faster in the 1×2–3H and the final l×1–2H phases.

Zero point energy effects as well as a H coverage dependent local interaction model could account for the observed effects.