Molecular rearrangement induced by hydrogen co-adsorption: C2H4 on Pd(110)

The symmetry of low-coverage (∼0.1 ML) ethylene adsorbed on Pd(110) and the co-adsorption effect of hydrogen have been investigated by high-resolution electron energy-loss spectroscopy. Ethylene adsorbs with π-bond character intact on both clean and H-covered Pd(110) with characteristic C–C stretching vibrational energies at 178 and 186 meV, respectively. The symmetry of the adsorbed ethylene, however, drastically changes upon the co-adsorption of hydrogen: the C–C axis which is tilted to the clean Pd(110) surface (C1 symmetry) is rearranged such that it becomes parallel to the H-covered Pd(110) surface (C2 symmetry).