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Surface Science 163 (1985) 503-515
North-Holland, Amsterdam 503
ELECTRONIC MODEL FOR ENERGIES, RELAXATIONS AND RECONSTRUCTION TRENDS AT METAL SURFACES D. TOMANEK and K.H. BENNEMANN
Institut ftir Theoretische Physik, Freie UniversitGt Berlin, Arnimallee 14, D - 1000 Berlin 33, Germany
Received 8 March 1985; accepted for publication 7 June 1985
A695
Surface energies and relaxations are calculated within the tight-binding formalism and includ-
ing also repulsive interatomic interactions. At fee and bee metal surfaces we obtain damped
oscillatory multilayer relaxations. Furthermore, we present results for the reconstruction at clean
(110) and (100) surfaces of Ir, Pt and Au. CO-suppressed and H-induced reconstruction observed
at some transition metal surfaces is quantitatively explained by coverage-dependent correction
terms to surface energies.
516 Surface Science 163 (1985) 516-540
North-Holland, Amsterdam
REACTION OF METHANOL WITH Cu(ll1) AND Cu(ll1) + O(ads)
J.N. RUSSELL, Jr., S.M. GATES and J.T. YATES, Jr.
SurJace Science Center, Department of Chemistry University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
Received 6 March 1985; accepted for publication 2 July 1985
The reactive chemistry of methanol on the Cu(ll1) surface, both with and without preadsorbed
oxygen atoms, is investigated between 190 and 700 K. The clean Cu(ll1) surface is inert, and
molecularly adsorbed methanol, the only stable surface species identified on this surface, desorbs
at about 210 K. Various trends are examined as a function of oxygen coverage, from the clean
surface to the saturation oxygen coverage (approximately 0.45 0 atom/Cu atom). The capacity of
the surface to adsorb methanol (190 K), and the formaldehyde yield ( - 400-450 K) are both
maximized when the oxygen coverage is about 0.26 0 atom/Cu atom. Trends in the yield of other
products, and the temperature for decomposition of the stable methoxy intermediate are examined.
Also. the rate of methoxy decomposition is limited by C-H bond breaking as evidenced by a
deuterium kinetic isotope effect.(C-H versus C-D). A minor decomposition path for methanol on
0 + Cu(ll1) involves CO, formation, probably via a formate surface intermediate. Preadsorbed
oxygen serves as an acceptor of the methanol hydroxyl hydrogen, enabling facile methanol
conversion to methoxy at low oxygen coverage for T >, 190 K. However, at high oxygen coverage
(e 2 0.26 0 atom/Cu atom) oxygen inhibifs surface reactivity. A two-dimensional model which
defines three types of surface sites is used to explain the general trend of methanol reactivity as a
function of oxygen coverage.