We report a combined X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and chronoamperometry (CA) study of formic acid electrooxidation on unsupported palladium nanoparticle catalysts in the particle size range from 9 to 40 nm. The CV CA measurements show that most active catalyst is made smallest (9 11 nm) Pd nanoparticles. Besides high reactivity, XPS data such nanoparticles display highest core-level binding energy (BE) shift valence band (VB) center downshift with respect...

We report an analysis of the interaction closed shell, lone pair ligands CO, NH3 and PF3 with a Cu surface. The surface is represented by one five atom clusters. analyzed constrained space orbital variation, CSOV, method which leads to division into several steps permits unambiguous assignment for energetic importance each step. σ repulsion between ligand metal demonstrated significance dipole moment shown. charge rearrangements are divided intra-unit polarization inter-unit donation units....

The hole states of O 2 +, obtained by ionization the oxygen molecule, have been examined theoretically in three approximations: (i) frozen orbital approximation, which consists single configuration calculations terms Hartree-Fock orbitals for neutral O2 molecule; (ii) direct hole-state g or u inversion symmetry is imposed on each molecular orbital; (iii) without restriction (ii). For 1s 4Σ− state approximations yield following potentials: 563.5 eV; 554.4 542.0 eV. experimental potential...

Abstract One of the long standing debates in actinide chemistry is level localization and participation 5 f valence orbitals covalent bonds across series. Here we illuminate role uranium, neptunium plutonium chemical bonding using advanced spectroscopies: M 4,5 HR-XANES 3 d 4 RIXS. Results reveal that are active for uranium neptunium, shown by significant variations their evidenced spectra. In contrast, appear localized surprisingly insensitive to different environments. We envisage this...

The origin and assignment of the complex main satellite X-ray photoelectron spectroscopy (XPS) features cations in ionic compounds have been subject extensive theoretical studies using different methods. There is agreement that within a molecular orbital model, one needs to take into account types configurations. Specifically, those where core electron removed, but no other configuration changes are made addition ionization, there also shake or charge-transfer configuration. However, strong...

Based on detailed theoretical analyses, we present, for the first time, direct evidence that significant interface dipole commonly observed atoms and molecules physisorbed metal surfaces originates from exchangelike effects. In case of Xe, previously proposed contributions chemical interactions do not play a role.

We have studied the strong variation of cluster-model binding energies CO/Cu(100) adsorbate system for clusters with between 1 and 34 atoms to represent Cu surface. Based on constrained space orbital approach metal-CO interaction is decomposed into three terms: (1) charge superposition free CO metal subunits, (2) polarization within (3) transfer subunits. The results show that one can identify bonding contributions which vary slowly cluster size shape. Further, relations representation...

The interaction of CO with Na, Mg, and Al surfaces has been studied using the molecular-orbital cluster model. These metals are chosen since we wish to study metal valence $\mathrm{sp}$ electrons in absence $d$ electrons. Our conclusion is that there substantial $\ensuremath{\sigma}$ repulsion bonding arises primarily from $\ensuremath{\pi}$ $2{\ensuremath{\pi}}^{*}$ donation. This based on analysis self-consistent-field calculations for linear $X\mathrm{CO}$ two-layer...

We report an unambiguous analysis of the metal–carbonyl bonding in Ni(CO)4 and Fe(CO)5 which gives new clear insight into importance various contributions to interaction. Three aspects interaction are particular importance: (i) The frozen orbital repulsion between metal 4s CO is large. This strongly favors Ni 3d10 Fe 3d8 occupations as starting point for interaction; (ii) π donation energetically much more important than σ donation. For Fe(CO)5, significant because 3d shell not filled it...

Our combined experimental and theoretical analysis of the shifts, with particle size, core-level binding energies (BE's) metal nanoparticles on insulating supports, shows that these shifts have an important initial state contribution arising, in large part, because lattice strain. This BE has not been recognized previously. Lattice strain changes chemical bonding between atoms this change induces shifts.

Analysis of ab initio cluster wave functions show that the shifts in vibrational frequencies CO/Cu and CN/Cu due to an applied electric field arise dominantly from a Stark effect. The CN bonding is largely ionic while CO has dative covalent \ensuremath{\pi} bond. Consequently effect mechanisms are significantly different.

The interaction of atomic fluorine and chlorine with the Si(111) surface has been studied by using clusters Si atoms to stimulate substrate. largest cluster contains ten atoms, representing first four layers surface. An F or Cl atom is added three high-symmetry adsorption sites. In on-top site, halogen adatom directly above a atom. open eclipsed sites are both threefold at center triangle first-layer atoms. fourth-layer while in site it second-layer Si. Ab initio Hartree-Fock wave functions...

The bonding in the 5,3Σ− and 3Δ states of FeCO, 3,1Σ+, 3Δ, 3 Π NiCO, 2Σ+ state CuCO are analyzed using constrained space orbital variation (CSOV) technique for both (CASSCF) SCF wave functions. is discussed terms σ repulsion between metal 4s CO 5σ, to donation when there an empty or partly occupied dσ 2π * backdonation. compared different metals states.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStructure and energetics of simple carbenes methylene, fluoromethylene, chloromethylene, bromomethylene, difluoromethylene, dichloromethyleneCharles W. Bauschlicher Jr., Henry F. Schaefer III, Paul S. BagusCite this: J. Am. Chem. Soc. 1977, 99, 22, 7106–7110Publication Date (Print):October 1, 1977Publication History Published online1 May 2002Published inissue 1 October...

Hartree-Fock calculations on linear NiCO and ${\mathrm{Ni}}_{2}$CO clusters have been used to model the local binding of CO upon adsorption Ni. The Ni-CO bond is determined by a mixing $\mathrm{CO}(5\ensuremath{\sigma})$ $\mathrm{Ni}(3d)$ orbitals; $\mathrm{Ni}(4s)$ electrons are not directly involved in as can be seen from orbital contour plots. A knowledge absolute relative shifts molecular ionization potentials their free-molecule values important for interpretation photoelectron spectra...

SCF ab-initio computations are performed for the ground states of CO2 and CO2−. The CO2− potential surfaces have been obtained over a large region space; in particular, intersection these two surfaces. Our results predict that stability depends strongly on whether it is formed near equilibrium bond angle (135°), most stable situation, or at significantly different angles. calculations show 6a1 molecular orbital diffuse character computed geometry (bond angle, 135.3°, length, 2.35 bohr)...

Both initial state effects, to a good approximation the electrostatic potential at nucleus, and final due response of electrons presence core-hole, contribute core-level binding energies, BE's. For Hartree-Fock, HF, wavefunctions, Koopmans' theorem, KT, which states that BE = -ε ιs rigorous. However, KT relationship is commonly used for Kohn-Sham, KS, ε's. We review with KS ε's fails give absolute contribution BE. we demonstrate shifts BE's from reference value are accurately obtained Thus...

Although the origin and assignment of complex XPS features cations in ionic compounds has been subject extensive theoretical work, agreement with experimental observations remains insufficient for unambiguous interpretation. This paper presents a rigorous ab initio treatment main satellite Fe 2p Fe2O3. possible using unique methodology selection orbitals that are used to form wavefunctions. orbital makes it treat both angular momentum coupling open shell core valence electrons as well shake...

The principal intent of this Perspective is to review the mechanisms that are responsible for shifts binding energies, ΔBE, observed in x-ray photoelectron spectroscopy (XPS) measurements and so relate electronic structure chemical bonding systems studied. To achieve goal, several theoretical considerations necessary beyond just calculation XPS BEs. Though briefly discussed here, we not primarily interested absolute values BE or quantitation using relative intensities. Within molecular...