Raman Scattering of C2H4 on Copper Films, Adsorbed at (111) Terraces and “Annealable Sites”

Ethylene adsorbed at (111) facets and at sites, which disappear by annealing to room temperature (probably (110) facets), has different vibrational frequencies and Raman cross-sections. By comparison with reflection−absorption infrared spectroscopy and high-resolution electron energy loss spectroscopy of ethylene on Cu(111), we have inferred the vibrational frequencies on perfect Cu(111). With respect to their position in solid ethylene, the vibrations with nuclear motion parallel to the (111) surface are within a few wavenumbers unshifted, whereas the CH 2 wagging mode with a motion of both carbon and hydrogen atoms perpendicular to the surface is shifted down by 60 cm - 1 . The “first layer effect” e.g. the large Raman cross-section of the adsorbed molecules with respect to molecules in the second and multiple layers, is demonstrated for the species at (110) and (111) facets.