Vibrational fine structure on C 1s core-level photoemission: Ni(1 1 1)–ethyne and Ni(1 1 1)–2-butyne

High-resolution core-level photoemission measurements for ethyne (HCCH) and 2-butyne (H3C–CC–CH3) on the Ni(1 1 1) surface reveal the presence of vibrational excitations for both adsorbates, similar to those observed in recent gas-phase core-level photoemission investigations. The vibrational line splitting for ethyne is 300±50 meV (2400±400 cm−1). A binding energy difference of approximately 0.7 eV was observed for the 1s core levels of the inequivalent C atoms in a monolayer of 2-butyne. The vibrational line splittings are 370±20 meV (2980±160 cm−1) and 250±30 (2020±240 cm−1) meV for the 289.56 and 288.80 eV core levels, respectively. In addition, preliminary energy-scanned photoelectron diffraction (PED) measurements were performed on a monolayer of 2-butyne. A comparison between the modulation functions of 2-butyne and previously measured ethyne indicates similar local structures for these adsorbates. Furthermore, the PED measurements reveal that the 288.80 eV C 1s line can be assigned to the central C atoms that participate in the bonding to the surface.