Adsorption Structure of Nitric Oxide on the Pt(111) Surface

Abstract

The adsorption structure of Pt(111) surface was studied by thermal desorption spectroscopy (TDS), infra-red absorption spectroscopy (IRAS), scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). LEED dynamical analysis, with the aid of other techniques, concluded that NO occupies the fcc hollow site at a low coverage, the fcc hollow and ontop sites at a medium coverage and the fcc hollow, ontop and hcp hollow sites at a high coverage, which is consistent with the other experimental and theoretical results. The desorption temperatures of NO on the fcc hollow (α species), ontop (β species) and hcp hollow sites (γ species) are 390, 300 and 200 K, respectively. The N-O stretching vibrations of each species are 1430-1490 cm-1, 1710 cm-1 and 1508 cm-1, respectively. Annealing to 250 K causes the desorption of the γ species, which results in the highly ordered two site occupied (α and β) surface. The high energy (>1 eV) electron injection from the STM tip causes the desorption of the β species, which enables us to get the surface of highly ordered α species. The mechanism of the desorption of the β species is the electron injection to the 2πa orbital, which has an anti-bonding character for the Pt-N bonding of the β species.