Unusual molecular orientation and frozen librational motion of C₆₀ on Cu(110)

Full-hemispherical angle-scanned x-ray photoelectron diffraction has been used to investigate the molecular orientation and librational motion of C₆₀ molecules adsorbed on the Cu(110) surface. The molecules are found to face the substrate surface in an unusual bonding configuration, rotating their symmetry axes by a few degrees away from the high-symmetry directions of the Cu(110) substrate. Despite the asymmetric molecular orientation, the C₆₀ molecules are immobile, i.e., they show no librational motion, up to temperatures well above the C₆₀ sublimation temperature.