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Photoelectron diffraction; Near edge extended X-ray absorption fine structure (NEXAFS); Chemisorption; Surface structure, morphology, roughness, and topography; Copper; Cyanogen; Oxygen; Low index single crystal surfaces
Abstract:
The adsorption geometry of CN on Cu(1 1 1), both with and without predosing with oxygen, has been investigated using N K-edge near-edge X-ray absorption fine structure (NEXAFS) and C 1s and N 1s scanned-energy mode photoelectron diffraction (PhD). The NEXAFS shows clearly that adsorbed onto clean Cu(1 1 1) the C–N axis is closely parallel to the surface, but in the presence of coadsorbed oxygen the average orientation has the axis tilted by 25° away from the surface; this confirms a much earlier report of an oxygen-induced reorientation of CN on this surface based on vibrational spectroscopy. The PhD data show very weak modulations which are rather insensitive to the emission geometry, clearly implying a high degree of disorder or a local adsorption site well-removed from any position of high point group symmetry. The best-fit structure corresponds to the CN lying slightly displaced from the three-fold coordinated hollow sites but with the C and N atoms having single Cu atom nearest neighbours at distances of 1.98 ± 0.05 and 2.00 ± 0.05 Å respectively.
