Determination of Site Specific Adsorption Energies of CO on Copper

Abstract

The binding energies of (isolated) CO molecules adsorbed at several atomic sites (terrace, step, kink) on a number of differently oriented copper surfaces have been measured by thermal desorption spectroscopy (TDS). In addition to the three low-indexed Cu surfaces several regular stepped and kinked single crystal surfaces have been employed. Using LEED measurements together with available data in the literature allowed identification of the various different CO adlayers and to assign the different TDS binding energies to the different adsorbate sites. For the close-packed surfaces binding energies between 47 kJ/mol (Cu(111)) and 51 kJ/mol (Cu(100)) were observed, which increased to 58 kJ/mol for CO molecules bound to step edges. Unexpectedly, for kink sites the same binding energy (to within 1 kJ/mol) as for step edges was observed. Moreover, a very similar binding energy of 58 kJ/mol was also measured for random defect sites on sputtered and on poly-crystalline substrates.