Identification of new adsorption sites of H and D on rhodium(100)

Abstract

Exposure of Rh(100) to hydrogen (deuterium) in atomic form leads to the population of adsorption sites, not attainable with molecular species. Quantitative thermal desorption spectroscopy (TDS), high resolution electron energy loss spectroscopy (HREELS), and density functional theory (DFT) calculations have been applied to investigate these new adsorption sites. In addition to the fourfold hollow sites (1 ML), which can be populated by dissociative adsorption, occupation of subsurface sites and the population of additional surface sites (for deuterium) have been observed (maximum coverage 3.4 ML). In TDS individual adsorption states show up in the form of three different peaks: Recombination of H (D) atoms from hollow sites around 300 K, desorption of subsurface species between 150–200 K, and recombinative desorption via a molecular precursor at about 120 K (for deuterium only). The exposure of the Rh(100) surface to atomic H (D) leads to a pronounced roughening of the surface, as evidenced in the HREELS spectra. Zero point corrected adsorption energies, activation barriers for adsorption, desorption, and diffusion into the subsurface sites, as well as vibrational energies have been calculated by DFT for a variety of adsorbate configurations of H and D and compared with the experimental data.