title: Two bonding configurations of acetylene on Si(001)-(2 x 1): a combined high-resolution electron energy loss spectroscopy and density functional theory study.
abstract: Two coexisting adsorption states of molecularly adsorbed acetylene on the Si(001)-(2 x 1) surface have been identified by a combined study based on the high-resolution electron energy loss spectroscopy and density functional computations. Seven possible adsorbate-substrate structures are considered theoretically including their full vibrational analysis. Based on a significantly enhanced experimental resolution, the assignment of 15 C2H2- and C2D2-derived vibrational modes identifies a dominant di-sigma bonded molecule adsorbed on top of a single Si-Si dimer. Additionally there is clear evidence for a second minority species which is di-sigma bonded between two Si-Si dimers within the same dimer row (end-bridge geometry). The possible symmetries of the adsorbate complexes are discussed based on the specular and off-specular vibrational measurements. They suggest lower than ideal C(2v) and C(s) symmetries for on-top and end-bridge species, respectively. At low coverages the symmetry reductions might be lifted.
authors.affiliation: Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria.
authors.forename: T
authors.initials: T
authors.lastname: Mineva
authors.forename: R
authors.initials: R
authors.lastname: Nathaniel
authors.forename: K L
authors.initials: KL
authors.lastname: Kostov
authors.forename: W
authors.initials: W
authors.lastname: Widdra