Adsorption bond length for H2O on TiO2(110): a key parameter for theoretical understanding.

Scanned-energy mode photoelectron diffraction results show the adsorption site of molecular water on TiO2(110) to be atop under-coordinated surface Ti atoms, confirming the results of total energy calculations and STM imaging. However, the Ti-O(water) bond length is 2.21 +/- 0.02 A, much longer than Ti-O bond lengths in strongly chemisorbed species on this surface, but significantly shorter than found in most total energy calculations. The need for theory to describe this weak bond effectively may be a key factor in the controversial problem of understanding this important surface reaction system.

Circular dichroism in core level photoemission from an adsorbed chiral molecule.

The results of experimental measurements and theoretical simulations of circular dichroism in the angular dependence (CDAD) of photoemission from atomic core levels of each of the enantiomers of a chiral molecule, alanine, adsorbed on Cu(110) are presented. Measurements in, and out of, substrate mirror planes distinguish CDAD due to the chirality of the sample and the experimental geometry. The effect due to sample chirality is relatively weak, so such measurements may not provide a routine spectral fingerprint of adsorbate chirality.

Bond lengths and bond strengths in weak and strong chemisorption: N2, CO, and CO/H on nickel surfaces.

New chemical-state-specific scanned-energy mode photoelectron diffraction experiments and density functional theory calculations, applied to CO, CO/H, and N2 adsorption on Ni(100), show that chemisorption bond length changes associated with large changes in bond strength are small, but those associated with changes in bond order are much larger, and are similar to those found in molecular systems. Specifically, halving the bond strength of atop CO to Ni increases the Ni-C distance by 0.06 A, but halving the bond order (atop to bridge site) at fixed bond strength causes an increase of 0.16 A.

Molecular adsorption bond lengths at metal oxide surfaces: failure of current theoretical methods.

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.