On the Structure of Chemisorbed Acetylene and Ethylene on Ni, Pd and Pt Surfaces

摘要

Filtered He II (hv = 40.8 eV) photoemission spectra for acetylene and ethylene molecularly chemisorbed at T approximately 100K on Ni(111), Ni(100), Pd(111) and Pt(111) have been obtained. The resulting vertical ionization potentials are presented and used within the framework of an approximate model to obtain information on the geometric structure of these molecules. Two initial state effects are discussed which are found to be important in deducing the molecular structures. These include an initial state shift of the lowest lying carbon-2s derived orbital and a metal atom induced shift of the sigma(cc) valence orbital for strong distorted species. The magnitudes of both effects are estimated - the later using Hartree-Fock LCAO calculations of Be interacting with acetylene or ethylene. The deduced geometries of chemisorbed ethylene are found to differ only slightly from those determined without considering these effects, but for acetylene two classes of structures are found. One class of structures is weakly distorted while the other is strongly distorted (approximately sp(2.5) hybridization). The latter structure is consistent with recent vibrational loss studies of chemisorbed ethylene on Ni shows relatively weak distortions. More subtle crystallographic and structural effects for acetylene and ethylene on (111), (100) and (110) Ni surfaces are also discussed. (Author)