Connie J. Nelin

• Independent Researcher

The principal concern of this paper is to compare theoretical predictions for M5 → 5f x-ray absorption spectroscopy (XAS) obtained between an isolated linear NpO2²⁺ model and an embedded NpO2²⁺ model that takes into account the environment of the solution where XAS measurements are actually conducted. The embedded model is an NpO2[H2O]5²⁺ cluster....

A detailed analysis of the N(1s) and C(1s) X-Ray Photoelectron Spectroscopy (XPS) is made, where the measured XPS is compared with theoretical Sudden Approximation (SA) intensities and theoretical XPS Binding Energies (BEs). There is remarkably good agreement between the theoretical predictions and the measured XPS; in particular, the different ful...

The features and the electronic character of the states for the Ni 2p x-ray photoelectron spectroscopy (XPS) of Ni(OH)2 were analyzed. This detailed analysis is based on ab initio molecular orbital wavefunctions for a cluster model of Ni(OH)2. The theory is validated by comparison with experiment. Then, advanced methods are used to explain and cont...

The principal intent of this Perspective is to review the mechanisms that are responsible for the shifts of binding energies, ΔBE, observed in x-ray photoelectron spectroscopy (XPS) measurements and so to relate the shifts to the electronic structure and the chemical bonding in the systems studied. To achieve this goal, several theoretical consider...

The origin and assignment of the complex main and satellite X-ray photoelectron spectroscopy (XPS) features of the cations in ionic compounds have been the subject of extensive theoretical studies using different methods. There is agreement that within a molecular orbital model, one needs to take into account different types of configurations. Spec...

The energy separation of the higher lying cation XPS binding energies, BEs, for MgO is examined. It is shown that the Hartree–Fock BEs overestimate the separation of the Mg BE(2s) and BE(2p), because an important many-body effect is neglected in the determination of the Hartree–Fock BEs. Once the many-body effect is taken into account, there is goo...

Although the origin and assignment of the complex XPS features of the cations in ionic compounds has been the subject of extensive theoretical work, agreement with experimental observations remains insufficient...

XPS analyses of open shell ionic compounds, especially oxides of the first row transition metals, for information such as oxidation state tend to focus on characteristics of the metal 2p XPS features alone. These analyses could be made considerably more robust with simultaneous characterization of the XPS of the metal 3p features as well as the 2p...

Based on both, ab-initio cluster calculations as well as periodic density functional based loss function calculations, we have assigned the origins of the valence electron excitation regime in electron energy loss spectra of well-ordered ceria films in (111) orientation at various states of reduction as well as after exposing the reduced films to h...

The Al K alpha, 1486.6 eV, based x-ray photoelectron spectroscopy (XPS) of Fe 2p and Fe 3p for Fe(III) in Fe2O3 and Fe(II) in FeO is compared with theoretical predictions based on ab initio wavefunctions that accurately treat the final, core-hole, multiplets. The principal objectives of this comparison are to understand the multiplet structure and...

The covalent character of the interaction between the metal cation and the oxygen ligands has been examined for two Fe oxides with different nominal oxidation states, Fe(II)O, and Fe(III)2O3. The covalent character is examined for the initial, ground state configuration and for the ionic states involving the removal of a shallow core, Fe 3p, and a...

The origins of the complex Fe 2p X-Ray Photoelectron Spectra (XPS) of hematite (α-Fe2O3) are analyzed and related to the character of the bonding in this compound. This analysis provides a new and novel view of the reasons for XPS binding energies (BEs) and BE shifts, which deepens the current understanding and interpretation of the physical and ch...

The relationship between the electronic structure of CaO and the binding energy, BE, shifts between surface and bulk atoms is examined and the physical origins of these shifts are established. Furthermore, the contribution of covalent mixing to the interaction, including the energetic importance, is investigated and found to be small. In particular...

The shifts of core-level binding energies can provide powerful information about the electronic structure of a material. Understanding the physical origin of these shifts for catalytically relevant oxides may provide important insight into their properties. This requires reliable theoretical methods which are able to relate the binding energy shift...

There is almost a factor of two increase in the FWHM of the main Ti2p1/2 XPS peak compared to the 2p3/2 in the closed shell Ti(IV) compounds TiO2 and strontium titanate, STO. Although the spectra of anatase and rutile forms of TiO2 differ slightly from STO, the 2p1/2 broadening over 2p3/2 is very similar. For STO, we show that ascribing this differ...

Important mechanisms that lead to features, often complex, in X-ray photoelectron spectroscopy (XPS) spectra are defined and described. It is shown that there is much information in an XPS spectrum that can be obtained by examining these features rather than examining only the shifts of main peaks between different materials. These mechanisms are p...

Cluster models of condensed systems are often used to simulate the core-level spectra obtained with X-Ray Photoelectron Spectroscopy, XPS, or with X-Ray Adsorption Spectroscopy, XAS, especially for near edge features. The main objective of this paper is to examine the dependence of the predicted L2,3 edge XAS of α-Fe2O3, an example of a high spin i...

We describe a detailed analysis of the features of the X-ray adsorption spectra at the Fe L2,3 edge of FeCl4⁻. The objective of this analysis is to explain the origin of the complex features in relation to properties of the wavefunctions, especially for the excited states. These properties include spin-orbit and ligand field splittings where a nove...

We have measured high-resolution core-level and valence-band x-ray photoemission spectra for single-crystal Ti2O3 cleaved anoxically. The Ti(III) spectra for this lattice are considerably more complex than those measured for Ti(IV)-based oxides due to the presence of a single unpaired electron in the conduction band. This open-shell electron config...

The U4f line is commonly used to determine uranium oxidation states with X-ray photoelectron spectroscopy (XPS). In contrast, the XPS of the shallow core-levels of uranium are rarely recorded. Nonetheless, theory has shown that the U 5d (and 5p) multiplet structure is very sensitive to oxidation state. In this contribution we extracted the U(IV) an...

Novel theoretical methods were used to quantify the magnitude and the energetic contributions of 4f/5f-O2p and 5d/6d-O2p interactions to covalent bonding in lanthanide and actinide oxides. Although many analyses have neglected the involvement of the frontier d orbitals, the present study shows that f and d covalencies are of comparable importance....

We describe a detailed theoretical analysis of how distortions from ideal cubic or Oh symmetry to tetrahedral, D4h, symmetry affect the shape, in particular the width, of the U L3-edge NEXAFS for U(vi) in octahedral coordination. The full-width-half-maximum (FWHM) of the L3-edge white line decreases with increasing distortion from Oh symmetry. In p...

Theoretical and experimental results for the surface core-level binding energy, BE, shifts, SCLS, for MgO(100) are presented and the anomalous O(1s) SCLS is interpreted in terms of the surface electronic structure. While the Mg(2p) surface BE shifts to a higher value than bulk by ≈ 1 eV as expected from the different surface and bulk Madelung poten...

Auger parameter (Δα) measurements have been employed to determine the extent to which initial- and final-state effects govern surface core-level shifts in x-ray photoelectron spectroscopy (XPS) measurements of Pd atoms confined between a bilayer SiO2 film and its Ru(0001) support. For atoms bound in this manner, we note negative binding energy shif...

Rigorous theoretical studies of the electronic structure to describe the Uranium L3 near edge X-ray absorption fine structure, NEXAFS, of different oxidation states of U in UOx are reported. Key features of the spectra are related to the ligand field splitting of the excited state orbitals. Furthermore, the ligand field splitting is related to the...

A rigorous study is presented of the physical processes related to X-Ray photoelectron spectroscopy, XPS, in the 4f level of U oxides, which, as well as being of physical interest in themselves, are representative of XPS in heavy metal oxides. In particular, we present compelling evidence for a new view of the screening of core-holes that extends p...

We review basic and advanced concepts needed for the correct analysis of XPS features. We place these concepts on rigorous foundations and explore their physical and chemical meanings without stressing the derivation of the mathematical formulations, which can be found in the cited literature. The significance and value of combining theory and expe...

The covalent character of ionic metal compounds, in particular oxides, may lead to substantial departures from nominal oxidation states. Since this covalent character changes the effective charge of the cation, it contributes to the chemical and physical properties of these compounds. A novel method of determining the degree of the covalent mixing...

Breathing: A simple and intuitive approach relates changes in bond lengths of core-hole ionized states to the extent of vibrational fine structure, or Franck-Condon broadening (ΔE), in X-ray photoelectron spectra of ionic compounds. For the extreme case of a monolayer of MgO on Ag(100), the difference in Franck-Condon broadening compared to bulk Mg...

The XPS of many oxides are quite complex and there may be several peaks of significant intensity for each subshell. These peaks arise from many-electron effects, which normally are treated with configuration interaction (CI) wavefunctions where static correlation effects are taken into account. It is common to use semiempirical methods to determine...

We present a rigorous parameter-free theoretical treatment of the Ce 4s and 5s photoelectron spectra of CeO2. The currently accepted model explains the satellite structure in the photoelectron spectra in terms of mixed valence (Ce 4f0 O 2p6, Ce 4f1 O 2p5, and Ce 4f2 O 2p4) configurations. We show that charge transfer (CT) into Ce 5d as well as conf...

Hartree-Fock stability equations for an open-shell configuration have been derived in the unitary-group formulation. These stability equations are used to compute a generalized open-shell random-phase approximation (OSRPA), where excited states are generated from the same multiplicity Hartree-Fock (HF) ground-state orbitals. This differs from conve...

Without Abstract

In this paper we provide an overview of IBM WebSphere Studio, a family of tools for developing distributed applications for J2EE™ servers for state-of-the-art information technology systems. In today's business environment such systems are complex, comprise multiple platforms, and make use of a wide range of technologies and standards. Through a re...

The World Wide Web offers a tremendous amount of information. Accessing and integrating the available information is a challenge. “Screen scraping” and reverse template engineering are manual and error-prone integration techniques from the past. The advent of Simple Object Access Protocol (SOAP) from the World Wide Web Consortium (W3C) allowed Web...

The explosion of the Internet and e-business in recent years has caused a secondary explosion in the amounts and types of information available to enterprise applications. Industry analysts predict that more data will be generated in the next three years than in all of recorded history. Because the adoption of Internet-based business transaction mo...

The molecular cluster model approach for the description of processes at surfaces is presented. It involves using finite clusters that contain surface atoms interacting with atomic or molecular adsorbates. Accurate ab initio wave functions can be obtained for the clusters, and, thus, this makes it possible to describe the bonding in terms that are...

Insitu infrared vibrational spectra of azide ions specifically adsorbed on polycrystalline silver electrodes immersed in aqueous electrolytes of composition 1 to 30 mM azide and 0.1 M perchlorate are reported for the potential range 0.25 to 0 V vs Ag/AgCl (3 M KCl). Adsorbed azide was not detected spectroscopically between 0 and −0.9 V, a range kno...

We have studied the coupling of the metal-ligand and the intramolecular-ligand stretching vibrations with ab initio cluster model wave functions. When there is no applied electric field, uncoupled internal coordinate modes and the fully coupled normal modes give essentially the same results. In the presence of an applied field, the coupling is impo...

The origin of the potential dependence of the high vibration frequency vCN is explained as a Stark effect. It is shown by means of abinitio cluster calculations that the coupling of vCN to the low frequency metal-ligand stretch plays a crucial role.

The nature of the bonding of the cyanide ligand to a metal atom and an organic group was examined through a study of the model systems CuCN, CuNC, CH3CN, and CH3NC. These particular molecules encompass extremes of bonding. Three properties of the wave functions are used to characterize the bond: (1) projection of the CN orbitals from the wave funct...

We have studied the strong variation of cluster-model binding energies of the CO/Cu(100) adsorbate system for clusters with between 1 and 34 atoms to represent the Cu surface. Based on the constrained space orbital variation approach the metal-CO interaction is decomposed into three terms: (1) charge superposition of the free CO and metal subunits,...

Scitation is the online home of leading journals and conference proceedings from AIP Publishing and AIP Member Societies

Scitation is the online home of leading journals and conference proceedings from AIP Publishing and AIP Member Societies

Analysis of ab initio cluster wave functions show that the shifts in the vibrational frequencies of 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 a dative covalent pi bond. Consequently the Stark effect mechanisms are significantly different.

A cluster model has been used to study the interaction of He with O/Ni(001) at c(2×2) coverage. The Ni11O2 cluster which was used contains two nearest-neighbor O atoms. The self-consistent-field interaction energies of He with this cluster, Ni11O2He, were obtained for several He geometries along the [100] direction between the He directly over an O...

A Comment on the Letter by Wimmer, Fu, and Freeman, Phys. Rev. Lett. 55, 2618 (1985).

The chemisorption of CO on Ni(100) is studied with a cluster model. The calculations suggest that chemisorption changes the nature of the Ni 3d orbitals. The open shell Ni 3d accepts charge from the Ni valence 4s4p orbitals, reducing the open shell 3d character on the Ni. The closed shell Ni 3d orbitals also mix with the Ni valence 4s4p orbitals an...

The bonding in the (5,3)Sigma - and 3Delta states of FeCO, the (3,1)Sigma + , 3Delta, and 3Pi states of NiCO, and the 2Sigma + state of CuCO are analyzed using the constrained-space orbital-variation (CSOV) technique for both (CASSCF) and SCF wave functions. The bonding is discussed in terms of sigma repulsion between the metals 4s and the CO 5-sig...

We discuss the nature and energy of the affinity levels of molecules on metals , on the basis of recent inverse photoemission experiments and ab-initio cluster calculations. We show that the energy and composition of the affinity levels such as the 2π* level of CO are not determined by the interaction of occupied d-band states with the empty adsorb...

Two distinctly different kinds of information can be obtained from ab initio wavefunctions. The v~lue of observables can be computed, quite accurately for relatively small systems, but this only complements experiment. However, the analysis and interpretation of wavefunctions can lead to conceptual understanding of the significance of measured valu...

The 4f core-level X-ray photoemission of small Pt clusters deposited on Teflon and SiO2 substrates has been investigated. The experimental results are discussed and related to other data reported in the literature. Parallel results are presented for ab initio selfconsistent field, SCF, calculations of the core ionization potentials, IPs, of small L...

The four low-lying states of WO were investigated and compared with similar states of CrO and MoO. For all these systems the ground state is 5 Pi, but the ordering of the upper states is different between WO and either CrO or MoO. The difference in the state ordering arises in part from the fact that in WO all of the states are formed from W(+) in...

Die Übergangsmetalloxide sind nahezu ionisch, mit einer negativen Ladung des Sauerstoffs von a 0.7 e′.

We have shown that there are serious limitations in the use of a one electron pseudopotential to describe the chemisorption of CO on a transition metal. Igel‐Mann and Stoll argue that the errors which we identified are due to our use of limited basis sets and to our neglect of corrections for the core–core interaction. We show that these claims are...

The transition-metal oxides are quite ionic; Mulliken population analyses for several oxides give a negative charge of about 0.7 electrons for oxygen. When the transition-metal d shell is only partially filled, the orbitals are involved in covalent bonds with O; both two-electron bonding (2)-antibonding (0) and one-electron bonding (2)-antibonding...

This paper addresses issues that should receive further examination in the near-term as concept selection for development of a U.S. space reactor power system is approached. The issues include: the economics, practicality and system reliability associated with transfer of nuclear spacecraft from low earth shuttle orbits to operational orbits, via c...

A major contribution to the shift of cluster core level binding energies with respect to cluster size is established. Core ionized cluster atoms with higher coordination have binding energies smaller than atoms with lower coordination. This is an initial state effect associated with the amount of valence charge density which surrounds the ionized a...

The interaction of CO with Cu5, Ni5, and Al4 are treated as model systems for molecular adsorption on metal surfaces. The effect of the use of pseudopotentials for the metal atoms is studied by considering three types of clusters. In the first case, all of the metal electrons are explicitly included in the wave function; an all electron (AE) treatm...

Research conducted during this period was focused on two main areas: (1) bonding in transition metal oxides; and (2) adsorption of CO on Al and Ni. In both of these theoretical studies a major interest was to obtain a better understanding of the nature of the bonding in transition metal containing systems. The studies used self consistent field (SC...

For the period of July 1982 through January 1983, the research carried out focused on the nature of metal adsorbate bonding. Two main areas were investigated in detail: (1) the adsorption of CO on Al, Na, Mg and Ni; and (2) bonding in transition metal oxides, CuO, CrO and MoO. These theoretical studies have lead to a new understanding of CO-metal b...

Cluster wavefunctions which have appropriate hybridization and polarization lead to reasonable properties for the interaction of an adsorbate with a solid surface. However, for Al clusters, it was found that the atomic change distribution is not uniform. The finite cluster size leads to changes not representative for an extended system. This effect...

Self consistent field and correlated wave functions have been computed for the ground and for several low-lying states of CuO. The ground state is X(2)PI and the lowest excited state, at approximately 8,000/cm above X(2)PI, is a previously unidentified 2-sigma(+) state. The separation of these states is compared to that for the similar states of KO...

Past Thermionic Fuel Element (TFE) inpile tests were examined to diagnose potential failure modes. Failure modes were analytically synthesized to reproduce observed test results. Design changes and recommended operating reactor conditions were determined and out-of-pile tests were recommended to enhance endurance of future TFE in-pile tests and ope...

The adsorption of CO on metal surfaces is represented by molecular orbital cluster models of CO at an on top site and adsorbed normal to the surface carbon end down. Ab initio SCF and MCSCF calculations are performed for several clusters. The new constrained space orbital variation CSOV approach is used to analyze the bonding and to compare CO adso...

Energies and XPS intensities of the three lowest N(1s) and O(1s) core-hole states of (NO)2 were calculated within the MC SCF framework. Relaxation effects which produce strong satellite structure, not present in the NO monomer, are characterized in terms of inter- and intra-unit screening. The results agree with the spectra of condensed NO on Ag(11...

Calculated CAS SCF potential curves are reported for the 3Σg− state of V2 and the 1Σg+ state of Cr2. At the CAS SCF level the 3Σg− state of V2 is calculated to be bound (Rc = 1.77 Å ωc = 593.6 cm−1, De 0.33 eV) and to involve a triple 3d bond; while the Cr2 potential curve is not bound but shows a shoulder near the experimental Re and the wave func...

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 the CO interaction with the metal valence sp electrons in the absence of d electrons. Our conclusion is that there is substantial σ repulsion and that the bonding arises primarily from the met...

It is noted that for molecular calculations, the basis sets presented by Huzinaga (1977) need to be augmented by (1) 5p functions to describe the 5s - 5p near degeneracy; (2) a diffuse 4d function to provide for a balanced description of the 5s2 4dn, 5s1 4d(n+1), and 4d(n+2) states of the atom; and (3) a set of 4f functions to correlate the 4d func...

A series of CAS SCF calculations are used to describe the lowest states of TiO. TiO is described as having polarized double bonds involving the Ti 3d orbitals. The nature of the excited states is discussed.

Accurate calculations of the dipole polarizability of F−, Ne, and F are performed by using the complete active space (CAS) SCF and externally contracted multireference configuration interaction (MC‐CCI) methods within the finite‐field perturbation scheme. The CAS SCF method gives the following polarizability results: 14.4, 2.63, and 3.68 a.u. for F...

The existence of a class of (very) high‐spin hydrocarbons is predicted on the basis of (a) new theorems for valence‐bond models, (b) classical structure theory, (c) standard theorems for molecular orbital theory, (d) several small‐system calculations with Hubbard and PPP Hamiltonians, and (e) a large‐system cluster expansion calculation applied to...

Second order MCSCF theory is presented in a unitary group formulation for any multiplicity without spin projection. Its reduction to lower order theory is discussed, as well as its extension through the use of effective Hamiltonians.

The unitary group formulation is a viable alternative to the Slater determinant and second quantized methods when the Hamiltonian is spinfree. Here the Hamiltonian is expressed as a second degree polynomial in the infinitesimal generators of U(ρ) where p is the number of spatial (spin-free) orbitals. Each irreducible space of U(ρ) is invariant unde...

We report and compare the π-ionization potentials of the 1-alkylfulvenes and the 1-alkylhexatrienes as computed by full CI, by first order Hartree—Fock and by Koopmans' theory using PPP and Hückel—Hubbard hamiltonians. These data provide the basis for a meaningful assessment of Koopmans' violations.

The theory of the open-and closed-shell restricted Hartree–Fock method is given a unitary group formulation. Both extremum and stability conditions are employed, the former leading to a generalized Brillouin theorem.