Probing the adsorption structure of a multifunctional organic molecule: a NIXSW and NEXAFS study of 3-chlorothiophene on Cu(111)

The adsorption structure of 3-chlorothiophene on Cu(lll) has been investiga ted using a combination of normal incidence X-ray standing wavefield absorp tion (NIXSW) and near edge X-ray absorption fine structure (NEXAFS) spectro scopy. For coverages up to saturation of the chemisorbed layer, the 3-chlor othiophene bonds through the S atom. The S atom adsorbs in an atop site wit h a Cu-S distance identical, within experimental error, to that observed fo r thiophene on the same substrate. From a combination of NEXAFS and NIXSW, thiophene was found to adsorb with the aromatic ring flat lying. From NIXSW measurements the S-Cl axis was found to be inclined by 12+/-2 degrees from the surface. Whilst NEXAFS data suggested an orientation of 23+/-8 degrees for the aromatic ring of 3-chlorothiophene. The CI atom interacted only we akly with the substrate, with a Cl-surface distance longer than the Cu-CI v an der Waal separation. (C) 1999 Published by Elsevier Science B.V. All lig hts reserved.