Vibrational analysis of the C 1s photoemission spectra from pure ethylidyne and ethylidyne coadsorbed with carbon monoxide on Rh(111)

High-resolution core-level photoemission with a resolution better than the intrinsic width of the C 1s level has been used to study pure and coadsorbed ethylidyne overlayers on Rh(111). Components due to excitation of the CH stretch vibration are clearly resolved in the C 1s spectra. In addition, a component due to the CC vibration of the ethylidyne molecules is identified. The asymmetry parameter is found to be similar for the two carbon atoms of the C2H3 molecule, indicating similar densities of states at the Fermi level for the two atoms. Coadsorption of ethylidyne with CO is found to induce a large C 1s binding-energy shift of the outer carbon atom of the ethylidyne. The remaining lineshape parameters, including the energy splits and intensity ratios of the CH vibrational progressions, are similar for the pure and coadsorbed ethylidyne.