The structure of benzene adsorbed on Pd(111): A dynamical LEED (Low-Energy Electron Diffraction) study

Coadsorption of benzene and CO on Pd(111) yields a new surface periodicity with (3 x 3) unit cell (relative to the (1 x 1) substrate periodicity). HREELS (High-Resolution Electron Energy Loss Spectroscopy) and TDS (Thermal Desorption Spectroscopy) imply that one benzene molecule and two CO molecules are adsorbed associatively over hollow sites in each (3 x 3) unit cell. This coadsorbed structure, Pd(111)-(3 x 3)-C/sub 6/H/sub 6/ + 2CO, was analyzed with dynamical calculations of LEED intensities to yield detailed bond lengths information. In this structure, both benzene and CO are adsorbed over fcc-type hollow sites in a close-packed lattice. The benzene ring skeleton is found to be nearly indistinguishable from the gas phase structure on Pd(111) surface. The molecular structure of benzene on Pd(111) obtained is compared with previously studied benzene structures on Rh(111) and Pt(111). In all cases, benzene is coadsorbed with CO to produce well-ordered superlattice. 18 refs., 1 fig., 1 tab.