The interaction of H (D) atoms with clean and D (H) covered Cu(111) surfaces was studied with TDS and direct product detection methods. H (D) atoms exhibit an initial sticking coefficient of 0.22. Due to abstraction, the surface saturation coverage is achieved at Θ=0.34, significantly less than the half monolayer coverage obtained through exposure of energetic H2 molecules to Cu(111) surfaces. Adsorbed H (D) desorbs recombinatively between 250 and 400 K. Desorption of absorbed H (D) via gaseous H2(D2) around 200 (210) K was observed according to a zero-order rate law with an activation energy of 0.40 (0.35) eV. Abstraction of D (H) by H (D) at 80 K lead to gaseous HD and D2(H2) formation. About 1% of the adsorbed species occurred in homonuclear products. Throughout the abstraction reaction the HD rate was found strictly proportional to coverage and flux, in line with a purely quasifirst-order, exponentially decreasing Eley–Rideal-type product rate. However, this phenomenology as well as the occurrence of homonuclear products can be explained by the exclusive action of hot-atom mechanisms, controlled by similar probabilities of reaction and sticking of hot atoms. The abstraction probabilities for adsorbed H or D, extrapolated to unity coverage, are 0.36 per incoming atom, the apparent abstraction cross-sections were obtained as σ=2.0 Å2 for H (ad) and D (ad). Abstraction is independent of temperature. Absorbed species are not extracted by incoming atoms.

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The kinetics of reactions which occur upon subjecting D(H) covered Ni(100) surfaces with H(D) atom fluxes were investigated. At 120 K surface temperature in the H→Dad reaction HD and D2 were observed as reaction products, in the D→Had reaction HD and H2 were reaction products. As the reaction temperature was well below the hydrogen desorption temperature, a direct reaction step, like in the Eley–Rideal (ER) mechanism, is suggested to operate for HD production. However, the characteristics of the HD formation kinetics observed in the present study contradict an essential element of the ER: mechanism the rate of HD formation is not proportional to the surface coverage of the adsorbed reaction species D or H under impact of a flux of H or D atoms. Therefore, a modification of the mechanistic description of atom/surface reactions seems necessary. This modification should allow for reaction products which are completely unaccounted for in the ER picture: D2 from H→Dad and H2 from D→Had reactions. The observed strong isotope effects in the reaction efficiencies support mechanisms in which the impinging gas phase atoms get trapped in the surface potential well prior to reaction.

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