Benzene on Pd(110): The first example of nonparallel adsorption

In contrast with previously reported examples of benzene chemisorbed on metal surfaces with parallel orientation, adsorption of a Pd(110) surface appears to produce a tilted ring. Polarized light angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) experiments in the mirror planes of the surface show that the adsorbate spectra give the expected strong polarization effects in the [001] azimuth but not in the [1¯10] azimuth. The azimuthal orientation of the ring is determined, and a tilt of the molecule of the order of 10°-20° into the grooves of the surface, towards [001] is proposed, so that the overall symmetry is reduced to $C_s$. A sharp $c(4\mathrm{}\times 2)$ lowenergy electron-diffraction (LEED) pattern is observed. The azimuthal orientation and the tilt determined from ARUPS are those required to minimize steric interactions in a model for the LEED pattern.