DAMPING OF MOLECULAR-MOTION ON A SOLID SUBSTRATE - EVIDENCE FOR ELECTRON-HOLE PAIR CREATION

The damping of molecular motion relative to a solid substrate was inve stigated by high-resolution vibrational spectroscopy in the far-infrar ed regime. For octane adsorbed on a hydrogen-passivated Ru(0001) surfa ce the experimental linewidths observed by He-atom scattering for the frustrated translation normal to the surface are in accord with a damp ing by phonon emission, but a strong broadening is found for the clean Ru substrate. This enhanced friction is related to an-increase in the rate of electron-hole (e-h) pair creation due to the presence of hybr id metal-molecule electronic states which are absent for the hydrogen passivated surface. Data from near-edge x-ray absorption spectroscopy provide direct evidence for these differences in electronic structure. Results from IR spectroscopy strongly suggest that the soft C-H bands observed for these systems are also related to the formation of these hybrid electronic states.