Structure determination of a [formula omitted] coadsorption phase on Ni(111)

Abstract

The structure of the Ni(111)(2 × 2)OCO adsorption phase, formed by CO adsorption onto a Ni(111)(2 × 2)O phase, has been determined by scanned-energy mode photoelectron diffraction of both the C 1s and O 1s signals. Contrary to earlier interpretation of vibrational spectroscopic data, the CO molecules occupy the same threefold coordinated hollow sites which they adopt on the clean Ni(111) surface, with a NiC bondlength of 1.95 ± 0.04 A ̊ and a CO bondlength of 1.17 ± 0.03 A ̊ . Changes in bondlength and the vibrational amplitude of the CO molecule against the surface are related to the weaker CO-metal bonding in the presence of the atomic oxygen. The chemisorbed oxygen atoms occupy the same “fcc” hollow sites, directly above third layer Ni atoms, both before and after CO adsorption.