NEXAFS investigations of cyclooctatetraene on TiO2(001)

Near-edge X-ray absorption fine structure (NEXAFS) was used to examine the nature of the adsorbed intermediate in the ring contraction of cyclooctatetraene (COT) to form benzene. Formation of aromatics by alkyne cyclotrimerization has been proposed to occur via a metallacyclopentadiene intermediate, and the chemistry of COT on reduced TiO2 surfaces has been suggested to occur via a complex exhibiting a similar bonding motif, although COT has been ruled out as a significant intermediate in alkyne cyclotrimerization. The conjugated structure of COT makes it an excellent subject for NEXAFS study, because of the ability of this technique to provide information about molecular hybridization and surface-adsorbate interactions, especially for species with Tr-orbitals. We have therefore applied this technique to probe the adsorbed intermediates in ring contraction and partial hydrogenation reactions of COT, and have compared our results with theoretical excitation spectra calculated from different models using time dependent density functional theory. This combination of experiment and theory provides new insights into the nature of the adsorbed intermediate involved in ring contraction and hydrogenation reactions of COT. (C) 2001 Elsevier Science B.V. All rights reserved.