Deprotonated Glycine on Cu(111): Quantitative Structure Determination by Energy-Scanned Photoelectron Diffraction

Abstract

The local adsorption site of the deprotonated simple amino acid glycine (glycinate) on Cu(111) has been investigated quantitatively by O 1s and N 1s energy-scanned photoelectron diffraction (PhD). The nitrogen atom is found to adsorb in a near-atop site with a Cu–N bond length of 2.02 ± 0.02 Å. However, based on the PhD data alone there is some ambiguity in the adsorption sites occupied by the oxygen atoms, although at least one of these atoms occupies a near-atop site with a Cu–O bond length of 2.00–2.02 ± 0.02–0.07 Å. Density functional theory (DFT) calculations have also been conducted on simple models (a low-coverage (3 × 3) phase of noninteracting molecules and a higher-coverage ordered (4 × 4) structure). The structural conclusions of the DFT calculations proved to be very sensitive to the use of different functionals and failed to resolve the structural ambiguity of the PhD analysis fully, but a single tridentate-bonding structural model appears to be most consistent with the PhD, DFT, and supporting spectroscopic information from previous studies.