Vibrational fine structure on C 1s core-level photoemission: Ni(111)-ethyne and Ni(111)-2-butyne

High-resolution core-level photoemission measurements for ethyne (HC drop C H) and 2-butyne (H3C-C dropC-CH3) on the Ni(111) surface reveal the presenc e of vibrational excitations for both adsorbates, similar to those observed in recent gas-phase core-level photoemission investigations. The vibration al line splitting for ethyne is 300 +/- 50 meV (2400 +/- 400 cm(-1)). A bin ding 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 vibrati onal line splittings are 370 +/- 20 meV (2980 +/- 160 cm(-1)) and 250 +/- 3 0 (2020 +/- 240 cm (1)) meV for the 289.56 and 288.80 eV core levels, respe ctively. 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 Is line can be assigned to the central C atoms that participate in the bonding to the surface. (C) 2001 E lsevier Science B.V. All rights reserved.