Berlin 2005 – scientific programme
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O: Oberflächenphysik
O 30: Adsorption an Oberfl
ächen III
O 30.2: Talk
Monday, March 7, 2005, 11:00–11:15, TU EB301
Calorimetric Measurements of the Heats of Adsorption of Aromatic Hydrocarbons on Pt(111) — •J.M. Gottfried1,2, H. Ihm2, H.M. Ajo2, P. Bera2, E.K. Vestergaard2, and C.T. Campbell2 — 1Lehrstuhl fuer Physikalische Chemie II, Universitaet Erlangen-Nuernberg, Egerlandstr. 3, D-91058 Erlangen — 2Department of Chemistry, Box 351700, University of Washington, Seattle, Washington 98195, USA
The heats of adsorption of benzene and naphthalene on clean Pt(111) at 300 K were measured by microcalorimetry [1]. The initial heats of adsorption were found to be 197 kJ/mol and 314 kJ/mol, respectively. Our data show that the initial and the integral heats are proportional to the number of carbon atoms in these aromatic systems, which lie parallel to the surface. Each bond between a sp2 hydridized C atom and the surface contributes 30 kJ/mol to the initial heat and 23 kJ/mol to the integral heat at 0.75 ML. Thus, our results disagree with recent DFT calculations [2], in which an integral heat of only 11 kJ/mol per C atom at 0.75 ML was obtained. Sticking probabilities were measured by a modified King and Wells method, giving initial values of 0.97 (benzene) and 0.99 (naphthalene). For both molecules, the sticking probability shows a Kisliuk-type behavior with increasing coverage, which implies that there are precursors to sticking, whose energetics have also been addressed. [1] H.M. Ajo, H. Ihm, D.E. Moilanen, C.T. Campbell, Rev. Sci. Instrum. 75 (2004) 4471. [2] C. Morin, D. Simon, P. Sautet, J. Phys. Chem. B 108 (2004) 12084.