Molecular Adsorption Bond Lengths at Metal Oxide Surfaces: Failure of Current Theoretical Methods

Abstract

New experimental structure determinations for molecular adsorbates on NiO(100) reveal much shorter Ni-C and Ni-N bond lengths for adsorbed CO and NH3 as well as NO (2.07, 1.88, 2.07 A) than previously computed theoretical values, with discrepancies up to 0.79 A, highlighting a major weakness of current theoretical descriptions of oxide-molecule bonding. Comparisons with experimentally determined bond lengths of the same species adsorbed atop Ni on metallic Ni(111) show values on the oxide surface that are consistently larger (0.1-0.3 A) than on the metal, indicating somewhat weaker bonding.

Probing the Basicity of Regular and Defect Sites of Alkaline Earth Metal Oxide Surfaces by BF3 Adsorption: A Theoretical Analysis

“…In particular, we have shown that various geometrical parameters exhibit a high degree of correlation with the basicity of the adsorption site, as measured by its IP. Since accurate measurements of bond lengths and bond angles are in principle available from near-edge extended X-ray absorption spectroscopy (NEXAFS), [39] we suggest that this kind of measurement can provide a direct way to titrate the donor properties of the surface. Another quantity which seems to nicely correlate with the surface basicity is the BÀF stretching frequency.…”

Oxidation electronics: bond–band–barrier correlation and its applications

“…The independent treatment of the correlated parameters often leads to an infinite number of numerical solutions [88][89][90]. In addition, theoretical calculations often consider the electrostatic interaction between the adsorbates and host atoms, being treated as rigid spheres, rather than the true bond formation [91], with essential contraction of bonds at the surface. Therefore, physical constraints on all the observations and their interdependence are necessary.…”

“…Exercises in terms of rigid adsorbate being trapped in the potential well at the surface without breaking the barrier seem to be less adequate in chemisorption studies. Recent photoelectron diffraction measurement [91] indicated that the bond lengths of CO, NO and NH 3 molecules are much shorter (by up to 0.79 Å ) on a Ni(001) and a NiO(001) surface than those determined by theoretical calculations and, therefore, the currently widely-used theoretical methods are questioned as in very serious errors in the particular cases [91]. It is pointed out that the shortened bond length indicates true bond formation, and not simply electrostatic interaction as has been concluded based on currently popular theoretical treatments [91].…”

Photoelectron diffraction: from phenomenological demonstration to practical tool

“…Perhaps the most startling example is provided by an early study of CO adsorption on NiO(100) (grown epitaxially on Ni(100)); the Ni-C bondlengths were found experimentally to be 2.07 Å, in sharp contrast to previous theoretical estimates of 2.46 Å and 2.86 Å [29 ]. While this adsorption system was known to present a substantial challenge to theoretical methods, these huge discrepancies in the structural parameters led to renewed efforts to improve the theory.…”