Showing papers on "Valence (chemistry) published in 2010"
TL;DR: An attosecond pump–probe measurement of the density matrix of valence electrons in atomic krypton ions is reported, able to completely characterize the quantum mechanical electron motion and determine its degree of coherence in the specimen of the ensemble.
Abstract: Chemical reactions are triggered by the dynamics of valence electrons in molecular orbitals. These motions typically unfold on a subfemtosecond scale and have eluded real-time access until now. Attosecond spectroscopy (an attosecond is 10−18 seconds), first applied to tracking electronic transitions from one quantum state to another, has now been extended to follow the hyperfast (subfemtosecond) motion of electron wavepackets in the valence shell — the bond-forming electrons — of krypton ions. This first proof-of-principle demonstration uses a simple system, but the expectation is that attosecond transient absorption spectroscopy of this type will ultimately reveal the elementary electron motions in molecules and solid-state materials that determine physical, chemical and biological properties. Attosecond technology (1 as = 10−18 S) promises the tools needed to directly probe electron motion in real time. These authors report attosecond pump–probe measurements that track the movement of valence electrons in krypton ions. This first proof-of-principle demonstration uses a simple system, but the expectation is that attosecond transient absorption spectroscopy will ultimately also reveal the elementary electron motions that underlie the properties of molecules and solid-state materials. The superposition of quantum states drives motion on the atomic and subatomic scales, with the energy spacing of the states dictating the speed of the motion. In the case of electrons residing in the outer (valence) shells of atoms and molecules which are separated by electronvolt energies, this means that valence electron motion occurs on a subfemtosecond to few-femtosecond timescale (1 fs = 10−15 s). In the absence of complete measurements, the motion can be characterized in terms of a complex quantity, the density matrix. Here we report an attosecond pump–probe measurement of the density matrix of valence electrons in atomic krypton ions1. We generate the ions with a controlled few-cycle laser field2 and then probe them through the spectrally resolved absorption of an attosecond extreme-ultraviolet pulse3, which allows us to observe in real time the subfemtosecond motion of valence electrons over a multifemtosecond time span. We are able to completely characterize the quantum mechanical electron motion and determine its degree of coherence in the specimen of the ensemble. Although the present study uses a simple, prototypical open system, attosecond transient absorption spectroscopy should be applicable to molecules and solid-state materials to reveal the elementary electron motions that control physical, chemical and biological properties and processes.
1,026 citations
TL;DR: In this paper, the dielectric properties of A2+B6+O4 (A2+: Ca, Pb, Ba; B6+: Mo, W) ceramics were investigated as a function of packing fraction and bond valence.
Abstract: Microwave dielectric properties of A2+B6+O4 (A2+: Ca, Pb, Ba; B6+: Mo, W) ceramics were investigated as a function of packing fraction and bond valence. For A2+B6+O4 specimens sintered at 800–1100 °C for 3 h, a single phase with a tetragonal scheelite structure was detected, and the theoretical density was higher than 93% throughout the composition. Although the ionic polarizability of Ba2+ ion was larger than that of Ca2+ ion, the dielectric constant (K) of BaB6+O4 showed a smaller value than that of CaB6+O4. These results could be attributed to changes of the packing fraction due to the effective ionic size. The Q·f value was largely dependent on the packing fraction, as well as the percentages of theoretical density. The temperature coefficients of the resonant frequencies (TCFs) of the specimens were affected by the bond valence of oxygen. The specimens of CaMoO4 sintered at 1000 °C for 3 h showed the K of 10.8, Q·f of 76,990 GHz and TCF of −22.8 ppm/°C, respectively.
362 citations
TL;DR: Goerigk et al. as mentioned in this paper presented an extension of their previously published benchmark set for low-lying valence transitions of large organic dyes, including two charged species and one with a clear charge-transfer transition.
Abstract: We present an extension of our previously published benchmark set for low-lying valence transitions of large organic dyes [L. Goerigk et al., Phys. Chem. Chem. Phys.11, 4611 (2009)]. The new set comprises in total 12 molecules, including two charged species and one with a clear charge-transfer transition. Our previous study on TD-DFT methods is repeated for the new test set with a larger basis set. Additionally, we want to shed light on different spin-scaled variants of the configuration interaction singles with perturbative doubles correction [CIS(D)] and the approximate coupled cluster singles and doubles method (CC2). Particularly for CIS(D) we want to clarify, which of the proposed versions can be recommended. Our results indicate that an unpublished SCS-CIS(D) variant, which is implemented into the TURBOMOLE program package, shows worse results than the original CIS(D) method, while other modified versions perform better. An SCS-CIS(D) version with a parameterization, that has already been used in an application by us recently [L. Goerigk and S. Grimme, ChemPhysChem9, 2467 (2008)], yields the best results. Another SCS-CIS(D) version and the SOS-CIS(D) method [Y. M. Rhee and M. Head-Gordon, J. Phys. Chem. A111, 5314 (2007)] perform very similar, though. For the electronic transitions considered herein, there is no improvement observed when going from the original CC2 to the SCS-CC2 method but further adjustment of the latter seems to be beneficial. Double-hybrid density functionals belong to best methods tested here. Particularly B2GP-PLYP provides uniformly good results for the complete set and is considered to be close to chemical accuracy within an ab initiotheory of color. For conventional hybrid functionals, a Fock-exchange mixing parameter of about 0.4 seems to be optimum in TD-DFT treatments of large chromophores. A range-separated functional such as, e.g., CAM-B3LYP seems also to be promising.
316 citations
TL;DR: In this paper, the authors report new solid state and hydrothermal synthetic routes to (Li,Na)2FePO4F that incorporate carbon-containing additives and result in good electrochemical properties of this Li ion electrode material.
Abstract: We report new solid state and hydrothermal synthetic routes to (Li,Na)2FePO4F that incorporate carbon-containing additives and result in good electrochemical properties of this Li (or Na) ion electrode material. Single crystal X-ray diffraction analysis of Na2FePO4F prepared by flux growth confirms the unusual structural features of this compound that include pairs of face-sharing metal octahedra and [6 + 1] coordination of the sodium ions. Facile Na−Li ion-exchange occurs upon reflux with lithium salts, upon electrochemical cycling in a cell (vs. Li), and also in a cell simply equilibrated at OCV. The material does not exhibit typical two-phase behavior on electrochemical cycling. A combination of a redox process which occurs with little structural strain, and ion scrambling give rise to a solid solution-like sloping voltage profile on charge−discharge, although localization of the Fe2+/3+ in the mixed valence single phase intermediate, Na1.5FePO4F drives a very small structural distortion. Temperature-d...
298 citations
TL;DR: In this article, a spray pyrolysis technique has been employed successfully for the synthesis of single phase mixed valence spinel hausmannite thin films using alcoholic start solution of manganese acetate (Mn(CH3COO)2·4H2O) on pyrex glass substrates at atmospheric pressure using air as a carrier gas.
287 citations
TL;DR: The spectra are found to be dominated by iron np to 1s electric dipole allowed transitions, with pronounced sensitivity to spin state, ligand identity, lig and ionization state, hybridization state and metal-ligand bond lengths.
Abstract: A systematic study of 12 ferric and ferrous Kβ X-ray emission spectra (XES) is presented. The factors contributing to the Kβ main line and the valence to core region of the spectra are experimentally assessed and quantitatively evaluated. While the Kβ main line spectra are dominated by spin state contributions, the valence to core region is shown to have greater sensitivity to changes in the chemical environment. A density functional theory (DFT) based approach is used to calculate the experimental valence spectra and to evaluate the contributions to experimental intensities and energies. The spectra are found to be dominated by iron np to 1s electric dipole allowed transitions, with pronounced sensitivity to spin state, ligand identity, ligand ionization state, hybridization state, and metal−ligand bond lengths. These findings serve as an important calibration for future applications to iron active sites in biological and chemical catalysis. Potential applications to Compound II heme derivatives are high...
231 citations
TL;DR: The effect of additional tight functions for Hartree-Fock and valence sp correlation was found to be surprisingly large, especially for the post-4d and post-5d elements.
Abstract: Correlation consistent basis sets that are suitable for the correlation of the outer-core (n−1)spd electrons of the post-d elements Ga–Rn have been developed. These new sets, denoted by cc-pwCVXZ-PP (X=D,T,Q,5), are based on the previously reported cc-pVXZ-PP sets that were built in conjunction with accurate small-core relativistic pseudopotentials (PPs) and designed only for valence nsp correlation. These new basis sets have been utilized in benchmark coupled cluster calculations of the core-valence correlation effects on the dissociation energies and spectroscopic properties of several small molecules. As expected, the most important contribution is the correlation of the (n−1)d electrons. For example, in the case of the group 13 homonuclear diatomics (Ga2,In2,Tl2), this leads to a dissociation energy increase compared to a valence-only treatment from 1.5 to 3.2 kcal/mol, bond length shortenings from −0.076 to −0.125 A, and harmonic frequency increases of 7–8 cm−1. Even in the group 15 cases (As2,Sb2,Bi2), the analogous effects of (n−1)d electron correlation are certainly not insignificant, the largest values being +4.4 kcal/mol, −0.049 A, and +9.6 cm−1 for the effects on De, re, and ωe, respectively. In general, the effects increase in magnitude down a group from 4p to 6p. Correlation of the outer-core (n−1)p electrons is about an order of magnitude less important than (n−1)d but larger than that of the (n−1)s. The effect of additional tight functions for Hartree–Fock and valence sp correlation was found to be surprisingly large, especially for the post-4d and post-5d elements. The pseudopotential results for the molecules containing post-3d elements are also compared to the analogous all-electron calculations employing the Douglas–Kroll–Hess Hamiltonian. The errors attributed to the PP approximation are found to be very small.
195 citations
TL;DR: In this article, Li ion insertion/extraction in valence tautomeric Prussian blue analogues AxMny[Fe(CN)6] (A: K, Rb) was investigated.
Abstract: The discovery of a new electrode material that provides a reversible Li ion insertion/extraction reaction is of primary importance for Li ion batteries. In this report, electrochemical Li ion insertion/extraction in valence tautomeric Prussian blue analogues AxMny[Fe(CN)6] (A: K, Rb) was investigated. Ex situ X-ray diffraction experiments revealed that the K salt without the valence tautomerism exhibits the Li ion insertion/extraction with a redox process of an Fe ion, while the Rb salt with the valence tautomerism exhibits that with a redox process of a Mn ion. Regardless of the redox-active metal ions, highly reversible Li ion storage was achieved. The electronic structure changes during the Li ion insertion/extraction are confirmed by XPS experiments.
163 citations
TL;DR: Both ferromagnetic and ferroelectric properties were observed in two enantiomerically pure nanoscale manganese cluster complexes supported by chiral Schiff base ligands.
Abstract: Both ferromagnetic and ferroelectric properties were observed in two enantiomerically pure nanoscale manganese cluster complexes supported by chiral Schiff base ligands, each of which comprises a 22-nucleus mixed-valence manganese(II/III) supratetrahedral cluster cation and an equilateral-triangle trinuclear manganese(III) cluster anion with C3 symmetry.
161 citations
TL;DR: In this paper, X-ray photoelectron spectroscopy (XPS) was used to visualize the occupied densities of states (DOS) in the valence band of LiFePO4.
Abstract: LiFePO4 has an interesting spin-polarized electronic structure showing a (3d↑)5(3d↓)1 electron configuration of the Fe2+ ion. In this work, we have experimentally evidenced the valence electronic structure of LiFePO4 and of its delithiated compound FePO4 by X-ray photoelectron spectroscopy (XPS), which allows a visualization of the occupied densities of states (DOS) in the valence band. XPS valence spectra were compared with the DOS obtained from DFT calculations by considering GGA and GGA + U approaches. Thanks to electrochemical extraction/insertion of Li+ ions in LiFePO4/FePO4, it was possible to display the Fe 3d spin-down electron of LiFePO4, which is not present in the valence spectrum of FePO4. We show that the study of XPS valence spectra is an efficient way to access the lithium insertion rate in LixFePO4 positive electrode materials for lithium-ion batteries. Besides the contribution to the Li-ion battery field, this paper is also a rare example of experimental evidence of a spin-resolved electr...
155 citations
TL;DR: In this paper, the band structure, bonding characteristics, and basic native defect configurations of hexagonal β-CuSCN are calculated. But the results do not conclusively confirm the predicted indirect nature of the lowest transitions.
Abstract: Copper thiocyanate (CuSCN) is a candidate as a transparent solid p-type conductor for optoelectronic and photovoltaic applications, such as solar cells. We calculate the band structure, bonding characteristics, and basic native defect configurations of hexagonal β-CuSCN. β-CuSCN is predicted to be an indirect-gap semiconductor with an unusual orbital character: although the highest valence bands have the expected character of Cu 3d levels hybridized with S 3p states, the conduction band minimum (at the K point of the hexagonal Brillouin zone) has mostly cyanide antibonding character. This quasi-molecular character results in some unusual properties, including that the electron effective masses are comparable to or even larger than the hole effective masses. Calculated results match well with the valence band spectrum of thin film CuSCN, although optical absorption measurements do not conclusively confirm the predicted indirect nature of the lowest transitions. The dominant p-type character of this materia...
TL;DR: In this paper, the effect of the dopant valence on the properties and catalytic behavior of Ni-based mixed metal oxides in the ethane oxidative dehydrogenation reaction was examined.
TL;DR: It is demonstrated that magnetic double exchange can be sustained by simple imidazolate bridging ligands, known to be well suited for the construction of coordination clusters and solids.
Abstract: The field of molecular magnetism has grown tremendously since the discovery of single-molecule magnets, but it remains centred around the superexchange mechanism. The possibility of instead using a double-exchange mechanism (based on electron delocalization rather than Heisenberg exchange through a non-magnetic bridge) presents a tantalizing prospect for synthesizing molecules with high-spin ground states that are well isolated in energy. We now demonstrate that magnetic double exchange can be sustained by simple imidazolate bridging ligands, known to be well suited for the construction of coordination clusters and solids. A series of mixed-valence molecules of the type [(PY5Me(2))V(II)(micro-L(br)) V(III)(PY5Me(2))](4+) were synthesized and their electron delocalization probed through cyclic voltammetry and spectroelectrochemistry. Magnetic susceptibility data reveal a well-isolated S = 5/2 ground state arising from double exchange for [(PY5Me(2))(2)V(2)(micro-5,6-dimethylbenzimidazolate)](4+). Combined modelling of the magnetic data and spectral analysis leads to an estimate of the double-exchange parameter of B = 220 cm(-1) when vibronic coupling is taken into account.
TL;DR: In this paper, the effect of K and K-Na substitution for Pb atoms in the rocksalt lattice of PbTe was investigated to test a hypothesis for development of resonant states in the valence band that may enhance the thermoelectric power.
Abstract: The effect of K and K-Na substitution for Pb atoms in the rocksalt lattice of PbTe was investigated to test a hypothesis for development of resonant states in the valence band that may enhance the thermoelectric power. We combined high-temperature Hall-effect, electrical conductivity, and thermal conductivity measurements to show that K-Na codoping do not form resonance states but can control the energy difference of the maxima of the two primary valence subbands in PbTe. This leads to an enhanced interband interaction with rising temperature and a significant rise in the thermoelectric figure of merit of p-type PbTe. The experimental data can be explained by a combination of a single- and two-band models for the valence band of PbTe depending on hole density that varies in the range of 1-15 x 10{sup 19} cm{sup -3}.
TL;DR: In this paper, a density-functional theory study on the electronic structure of pure and 3D transition metal (TM) (Sc, Ti, Cr, Mn, and Ni) incorporated α-Fe2O3 is presented.
Abstract: We present a density-functional theory study on the electronic structure of pure and 3d transition metal (TM) (Sc, Ti, Cr, Mn, and Ni) incorporated α-Fe2O3. We find that the incorporation of 3d TMs in α-Fe2O3 has two main effects such as: (1) the valence and conduction band edges are modified. In particular, the incorporation of Ti provides electron carriers and reduces the electron effective mass, which will improve the electrical conductivity of α-Fe2O3. (2) The unit cell volume changes systematically such as: the incorporation of Sc increases the volume, whereas the incorporation of Ti, Cr, Mn, and Ni reduces the volume monotonically, which can affect the hopping probability of localized charge carriers (polarons). We discuss the importance of these results in terms of the utilization of hematite as a visible-light photocatalyst.
TL;DR: In this article, a photoinduced low-spin to high-spin conversion in the Fe(II) polypyridyl complex [Fe(tren(py)(3))] was studied via picosecond soft X-ray spectroscopy.
Abstract: Solution-phase photoinduced low-spin to high-spin conversion in the Fe(II) polypyridyl complex [Fe(tren(py)(3))](2+) (where tren(py)(3) is tris(2-pyridylmethyliminoethyl)amine) has been studied via picosecond soft X-ray spectroscopy. Following (1)A(1) --> (1)MLCT (metal-to-ligand charge transfer) excitation at 560 nm, changes in the iron L(2)- and L(3)-edges were observed concomitant with formation of the transient high-spin (5)T(2) state. Charge-transfer multiplet calculations coupled with data acquired on low-spin and high-spin model complexes revealed a reduction in ligand field splitting of approximately 1 eV in the high-spin state relative to the singlet ground state. A significant reduction in orbital overlap between the central Fe-3d and the ligand N-2p orbitals was directly observed, consistent with the expected ca. 0.2 A increase in Fe-N bond length upon formation of the high-spin state. The overall occupancy of the Fe-3d orbitals remains constant upon spin crossover, suggesting that the reduction in sigma-donation is compensated by significant attenuation of pi-back-bonding in the metal-ligand interactions. These results demonstrate the feasibility and unique potential of time-resolved soft X-ray absorption spectroscopy to study ultrafast reactions in the liquid phase by directly probing the valence orbitals of first-row metals as well as lighter elements during the course of photochemical transformations.
TL;DR: In this paper, a structural transition from rhombohedral R 3 c to orthorhombic P 4 m m occurred in pure BiFeO3 (BFO), 15% Nd doped BFO (BNF), and 15% nd and 2% high-valence Mn co-doped (BNFM) multiferroic ceramics were prepared by a rapid liquid phase sintering technique.
Journal Article•
TL;DR: The results demonstrate the feasibility and unique potential of time-resolved soft X-ray absorption spectroscopy to study ultrafast reactions in the liquid phase by directly probing the valence orbitals of first-row metals as well as lighter elements during the course of photochemical transformations.
Abstract: Solution-phase photoinduced low-spin to high-spin conversion in the FeII polypyridyl complex [Fe(tren(py)3)]2+ (where tren(py)3 is tris(2-pyridylmethyliminoethyl)amine) has been studied via picosecond soft X-ray spectroscopy Following 1A1 --> 1MLCT (metal-to-ligand charge transfer) excitation at 560 nm, changes in the iron L2- and L3-edges were observed concomitant with formation of the transient high-spin 5T2 state Charge-transfer multiplet calculations coupled with data acquired on low-spin and high-spin model complexes revealed a reduction in ligand field splitting of 1 eV in the high-spin state relative to the singlet ground state A significant reduction in orbital overlap between the central Fe-3d and the ligand N-2p orbitals was directly observed, consistent with the expected ca 02 Angstrom increase in Fe-N bond length upon formation of the high-spin state The overall occupancy of the Fe-3d orbitals remains constant upon spin crossover, suggesting that the reduction in sigma-donation is compensated by significant attenuation of pi-back-bonding in the metal-ligand interactions These results demonstrate the feasibility and unique potential of time-resolved soft X-ray absorption spectroscopy to study ultrafast reactions in the liquid phase by directly probing the valence orbitals of first-row metals as well as lighter elements during the course of photochemical transformations
TL;DR: In this article, the In 3D core line was measured at hv = 1486.6 eV for both undoped and Sn-doped In(2)O(3) and it was shown that structure derived from electronic levels with significant In or Sn 5s character is selectively enhanced under 6000 eV excitation.
Abstract: The valence and core levels of In(2)O(3) and Sn-doped In(2)O(3) have been studied by hard x-ray photoemission spectroscopy (hv = 6000 eV) and by conventional Al K alpha (hv = 1486.6 eV) x-ray photoemission spectroscopy. The experimental spectra are compared with density-functional theory calculations. It is shown that structure deriving from electronic levels with significant In or Sn 5s character is selectively enhanced under 6000 eV excitation. This allows us to infer that conduction band states in Sn-doped samples and states at the bottom of the valence band both contain a pronounced In 5s contribution. The In 3d core line measured at hv = 1486.6 eV for both undoped and Sn-doped In(2)O(3) display an asymmetric lineshape, and may be fitted with two components associated with screened and unscreened final states. The In 3d core line spectra excited at hv = 6000 eV for the Sn-doped samples display pronounced shoulders and demand a fit with two components. The In 3d core line spectrum for the undoped sample can also be fitted with two components, although the relative intensity of the component associated with the screened final state is low, compared to excitation at 1486.6 eV. These results are consistent with a high concentration of carriers confined close to the surface of nominally undoped In(2)O(3). This conclusion is in accord with the fact that a conduction band feature observed for undoped In(2)O(3) in Al K alpha x-ray photoemission is much weaker than expected in hard x-ray photoemission.
TL;DR: In this paper, the authors showed that the distribution of the cations within the spinel lattice of the ferrite nanoparticles, and consequently their magnetic properties are strongly affected by the synthesis method used.
Abstract: The Co–ferrite nanoparticles having a relatively uniform size distribution around 8 nm were synthesized by three different methods. A simple co-precipitation from aqueous solutions and a co-precipitation in an environment of microemulsions are low temperature methods (50 °C), whereas a thermal decomposition of organo-metallic complexes was performed at elevated temperature of 290 °C. The X-ray diffractometry (XRD) showed spinel structure, and the high-resolution transmission electron microscopy (HRTEM) a good crystallinity of all the nanoparticles. Energy-dispersive X-ray spectroscopy (EDS) showed the composition close to stoichiometric (~CoFe2O4) for both co-precipitated nanoparticles, whereas the nanoparticles prepared by the thermal decomposition were Co-deficient (~Co0.6Fe2.4O4). The X-ray absorption near-edge structure (XANES) analysis showed Co valence of 2+ in all the samples, Fe valence 3+ in both co-precipitated samples, but average Fe valence of 2.7+ in the sample synthesized by thermal decomposition. The variations in cation distribution within the spinel lattice were observed by structural refinement of X-ray absorption fine structure (EXAFS). Like the bulk CoFe2O4, the nanoparticles synthesized at elevated temperature using thermal decomposition displayed inverse spinel structure with the Co ions occupying predominantly octahedral lattice sites, whereas co-precipitated samples showed considerable proportion of cobalt ions occupying tetrahedral sites (nearly 1/3 for the nanoparticles synthesized by co-precipitation from aqueous solutions and almost 1/4 for the nanoparticles synthesized in microemulsions). Magnetic measurements performed at room temperature and at 10 K were in good agreement with the nanoparticles’ composition and the cation distribution in their structure. The presented study clearly shows that the distribution of the cations within the spinel lattice of the ferrite nanoparticles, and consequently their magnetic properties are strongly affected by the synthesis method used.
TL;DR: In this article, a comparative scanning tunneling microscopy (STM) analysis of the atomic-scale structure and morphology of MoS 2 nanoclusters doped with the first-row transition metals: Fe, Co, Ni, and Cu was performed.
TL;DR: In the paragraph following eq 28, the average bond valence was incorrectly referred to as V/R. It has been corrected to V/N as mentioned in this paper, and the paper originally posted to the web on September 3, 2009, and was reposted on September 24, 2009.
Abstract: In the paragraph following eq 28, the average bond valence was incorrectly referred to as V/R. It has been corrected to V/N. The paper originally posted to the web on September 3, 2009, and was reposted on September 24, 2009.
TL;DR: In this paper, a single phase ceramics of pure cobalt and manganese oxide spinels were characterized by neutron powder diffraction over the whole solid solution range, showing that cobalt is preferentially substituted on the tetrahedral site for x < 1, then on the octahedral site to increase x values.
TL;DR: Examples of typical applications of EPR comprise transition metal ions in paramagnetic valence states such as vanadium, radical anions formed on oxide surfaces and electrons in ferromagnetic particles such as nickel as well as in conduction bands of organic conductors such as polyaniline.
Abstract: Electron Paramagnetic Resonance (EPR) offers widespread opportunities for monitoring catalytically relevant species that contain unpaired electrons under conditions close to those of heterogeneous catalytic gas and liquid phase reactions. In this tutorial review, after introducing basic theoretical and experimental principles of the technique, selected examples of typical applications are discussed that comprise (1) transition metal ions in paramagnetic valence states such as vanadium, (2) radical anions such as O˙− formed on oxide surfaces and (3) electrons in ferromagnetic particles such as nickel as well as in conduction bands of organic conductors such as polyaniline.
TL;DR: An element-selective study of the occupied and unoccupied density of electronic states in Pt nanoparticles was performed using hard X-ray resonant inelasticX-ray scattering (RIXS) and an opening in the valence d band is observed when CO is adsorbed.
Abstract: An element-selective study of the occupied and unoccupied density of electronic states in Pt nanoparticles was performed using hard X-ray resonant inelastic X-ray scattering (RIXS). An opening in the valence d band is observed when CO is adsorbed. The gap originates from bonding and antibonding orbitals between Pt and CO. The adsorption of CO blocks sites and changes the electronic structure, thus further passivating the catalytic activity of Pt. The experimental results are supported by full multiple scattering calculations.
TL;DR: In this article, the effect of glass matrix modifiers on color and d-d electron spectra of chosen transition metal ions was analyzed using the analysis of colour and electron spectras of the obtained glasses, and it was shown that the chemical composition of the glass matrix influences the coordination state of the transition metal.
TL;DR: This analysis was based on a recently developed method that combines the extended transition state scheme with the theory of natural orbitals for chemical valence (ETS-NOCV) and finds that hydrogen bonding is associated with charge rearrangement in both the electronic sigma-framework (Deltarho(sigma) and the electronic pi-framework(pi).
Abstract: We have analyzed hydrogen bonding in a number of species, containing from two to four hydrogen bonds. The examples were chosen in such a way that they would enable us to examine three different hydrogen bonds involving OH−O, NH−O, and NH−N. A common feature of the investigated systems is that they all are expected to exhibit resonance assisted hydrogen bonding (RAHB) in the electronic π-framework. Our analysis was based on a recently developed method that combines the extended transition state scheme with the theory of natural orbitals for chemical valence (ETS-NOCV). We find that hydrogen bonding is associated with charge rearrangement in both the electronic σ-framework (Δρσ) and the electronic π-framework (Δρπ). However the stabilization due to Δρσ is four times as important as the stabilization (RAHB) due to Δρπ. Stabilization due to the electrostatic interaction (ΔEelstat) between the two monomers that are brought together to form the hydrogen bonds is also important. However ΔEel cannot alone account...
Book•
01 Jan 2010TL;DR: In this article, some basic notions of the classical and quantum statistical physics have been discussed, e.g., Bose-condensation, general theory of phase transitions, Bose and Fermi-statistics, Phonons in crystals, magnetic impurities in metals, Kondo effect, heavy fermions and mixed valence References Index.
Abstract: 1. Some basic notions of the classical and quantum statistical physics 2. General theory of phase transitions 3. Bose- and Fermi-statistics 4. Phonons in crystals 5. General Bose-systems: Bose-condensation 6. Magnetism 7. Electrons in metals 8. Interacting electrons: Green functions and Feynman diagrams (methods of the field theory in many-particle physics) 9. Electrons with Coulomb interaction 10. Fermi-liquid theory and its possible generalizations 11. Instabilities and phase transitions in electronic systems 12. Strongly correlated electrons 13. Magnetic impurities in metals, Kondo effect, heavy fermions and mixed valence References Index.
TL;DR: In this article, in situ electron energy-loss spectroscopy and first-principles density functional theory calculations are used to distinguish between metallic Co, Co3O4, as well as CoO.
Abstract: Determining the Co valence, particularly in Co-based nanocatalysts is a longstanding experimental challenge. In this paper, we utilize in situ electron energy-loss spectroscopy and first-principles density functional theory calculations to distinguish between metallic Co, Co3O4, as well as CoO. More specifically, differences in the O K- and Co L-edges are utilized to determine the Co valence in different Co-oxide particles. We will further demonstrate that while the metallic Co L3/L2-ratio equals that of partially reduced Co3O4, the near-edge fine-structure of the metallic Co L-edge exhibits additional features not present in any Co-oxide. The origin of these features will be discussed. Based on our experimental and theoretical results, we will propose a fitting method to distinguish metallic Co from Co-oxides.
TL;DR: In this article, the relaxation pathways of photoinduced electronic redistribution at nanostructured semiconductor surfaces are obtained from time-dependent density matrix and ab initio electronic structure methods, giving electronic changes in energy and space over time.
Abstract: Relaxation pathways of photoinduced electronic redistribution at nanostructured semiconductor surfaces are obtained from time-dependent density matrix and ab initio electronic structure methods, giving electronic changes in energy and space over time. They are applied to a Ag cluster on a Si(111) surface, initially photoexcited by a short pulse, and show that the Ag cluster adds surface-localized states that enhance electron transfer. Results on the time evolution of population density distributions in energy and in space, for valence and conduction bands, explore the energy band landscape of a Si slab, with various relaxation pathways ending up in a charge-separated state, with a hole in the Si slab and an electron in the adsorbed Ag cluster. Calculated electronic relaxation times for Si(111)/H are of the same order as experimental values for similar semiconductor systems.