| 1. |
- Mijovilovich, Ana, et al.
(författare)
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The Interpretation of Sulfur K-edge XANES spectra: A case Study on Thiophene and Aliphatic Sulfur Compounds
- 2009
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455 .- 1089-5639 .- 1520-5215. ; 113, s. 2750-2756
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Tidskriftsartikel (refereegranskat)abstract
- Sulfur K-edge XANES has been measured for three sulfur model compounds, dibenzothiophene, dibenzothiophene sulfone, and aliphatic sulfur (DL-methionine). The spectra have been simulated with Density Functional Theory (DFT) using a number of methods, including the half core hole approximation. Dipole transition elements were calculated and the transitions were convoluted with linearly increasing Gaussian functions in the first 20 eV of the near edge region. In the case of dibenzothiophene, relaxation of the first excited states in the presence of the core-hole gave a further improvement. The theoretical results reproduce well the features of the spectra and give insight in the relation between geometric structure and molecular orbitals. Though DL-methionine and dibenzothiophene show a similar sharp rise of the white line, their molecular levels are quite different, pointing out the difficulties in finding useful “fingerprints” in the spectra for specific compounds.
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| 2. |
- Malysheva, Lyuba, et al.
(författare)
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Molecular Orientation in Helical and All-Trans Oligo(ethylene glycol)-Terminated Assemblies on Gold: Results of ab Initio Modeling
- 2005
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215 .- 1520-6106 .- 1520-5207. ; 109:34, s. 7788-7796
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Tidskriftsartikel (refereegranskat)abstract
- The structural properties of self-assembled monolayers (SAMs) of oligo(ethylene glycol) (OEG)-terminated and amide-containing alkanethiols (HS(CH2)15CONH(CH2CH2O)6H and related molecules with shorter alkyl or OEG portions) on gold are addressed. Optimized geometry of the molecular constituents, characteristic vibration frequencies, and transition dipole moments are obtained using density-functional theory methods with gradient corrections. These data are used to simulate IR reflection-absorption (RA) spectra associated with different OEG conformations. It is shown that the positions and relative intensities of all characteristic peaks in the fingerprint region are accurately reproduced by the model spectra within a narrow range of the tilt and rotation angles of the alkyl plane, which turns out to be nearly the same for the helical and all-trans OEG conformations. In contrast, the tilt of the OEG axis changes considerably under conformational transition from helical to all-trans OEG. By means of ab initio modeling, we also clarify other details of the molecular structure and orientation, including lateral hydrogen bonding, the latter of which is readily possessed by the SAMs in focus. These results are crucial for understanding phase and folding characteristics of OEG SAMs and other complex molecular assemblies. They are also expected to contribute to an improved understanding of the interaction with water, ions, and ultimately biological macromolecules.
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| 3. |
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| 4. |
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| 5. |
- Abb, Marcel J.S., et al.
(författare)
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Thermal Stability of Single-Crystalline IrO2(110) Layers : Spectroscopic and Adsorption Studies
- 2020
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:28, s. 15324-15336
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of ultrathin single-crystalline IrO2(110) films with the gas phase proceeds via the coordinatively unsaturated sites (cus), in particular Ircus, the undercoordinated oxygen species on-top O (Oot) that are coordinated to Ircus, and bridging O (Obr). With the combination of different experimental techniques, such as thermal desorption spectroscopy, scanning tunneling microscopy (STM), high-resolution core-level spectroscopy (HRCLS), infrared spectroscopy, and first-principles studies employing density functional theory calculations, we are able to elucidate surface properties of single-crystalline IrO2(110). We provide spectroscopic fingerprints of the active surface sites of IrO2(110). The freshly prepared IrO2(110) surface is virtually inactive toward gas-phase molecules. The IrO2(110) surface needs to be activated by annealing to 500-600 K under ultrahigh vacuum (UHV) conditions. In the activation step, Ircus sites are liberated from on-top oxygen (Oot) and monoatomic Ir metal islands are formed on the surface, leading to the formation of a bifunctional model catalyst. Vacant Ircus sites of IrO2(110) allow for strong interaction and accommodation of molecules from the gas phase. For instance, CO can adsorb atop on Ircus and water forms a strongly bound water layer on the activated IrO2(110) surface. Single-crystalline IrO2(110) is thermally not very stable although chemically stable. Chemical reduction of IrO2(110) by extensive CO exposure at 473 K is not observed, which is in contrast to the prototypical RuO2(110) system.
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| 6. |
- Abbas, Zareen, 1962, et al.
(författare)
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Size-Dependent Surface Charging of Nanoparticles
- 2008
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Ingår i: J of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:15, s. 5715-5723
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Tidskriftsartikel (refereegranskat)abstract
- Experimental interest in the possible curvature dependence of particle charging in electrolyte solutions is subjected to theoretical analysis. The corrected Debye-Hückel theory of surface complexation (CDH-SC) and Monte Carlo (MC) simulation are applied to investigate the dependence of surface charging of metal oxide nanoparticles on their size. Surface charge density versus pH curves for spherical metal oxide nanoparticles in the size range of 1-100 nm are calculated at various concentrations of a background electrolyte. The surface charge density of a nanoparticle is found to be highly size-dependent. As the particle diameter drops to below 10 nm there is considerable increase in the surface charge density as compared with the limiting values seen for particles larger than 20 nm. This increase in the surface charge density is due to the enhanced screening efficiency of the electrolyte solution around small nanoparticles, which is most prominent for particles of diameters less than 5 nm. For example, the surface charge densities calculated for 2 nm particles at 0.1 M concentration are very close to the values obtained for 100 nm particles at 1 M concentration. These predictions of the dependence of surface charge density on particle size by the CDH-SC theory are in very good agreement with the corresponding results obtained by the MC simulations. A shift in the pH value of the point of zero charge toward higher pH values is also seen with a decreasing particle size.
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| 7. |
- Abid, Abdul Rahman, et al.
(författare)
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Forming Bonds While Breaking Old Ones : Isomer-Dependent Formation of H3O+ from Aminobenzoic Acid During X-ray-Induced Fragmentation
- 2023
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 127:6, s. 1395-1401
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Tidskriftsartikel (refereegranskat)abstract
- Intramolecular hydrogen transfer, a reaction where donor and acceptor sites of a hydrogen atom are part of the same molecule, is a ubiquitous reaction in biochemistry and organic synthesis. In this work, we report hydronium ion (H3O+) production from aminobenzoic acid (ABA) after core-level ionization with soft X-ray synchrotron radiation. The formation of H3O+ during the fragmentation requires that at least two hydrogen atoms migrate to one of the oxygen atoms within the molecule. The comparison of two structural isomers, ortho- and meta-ABA, revealed that the production of H3O+ depends strongly on the structure of the molecule, the ortho-isomer being much more prone to produce H3O+. The isomer-dependency suggests that the amine group acts as a donor in the hydrogen transfer process. In the case of ortho-ABA, detailed H3O+ production pathways were investigated using photoelectron-photoion-photoion coincidence (PEPIPICO) spectroscopy. It was found that H3O+ can result from a direct two-body dissociation but also from sequential fragmentation processes.
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| 8. |
- Abid, Jean-Pierre, et al.
(författare)
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Controlled reversible adsorption of core : Shell metallic nanoparticles at the polarized water/1,2-dichloroethane interface investigated by optical second-harmonic generation
- 2007
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:25, s. 8849-8855
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Tidskriftsartikel (refereegranskat)abstract
- We report the observation of the reversible adsorption of core-shell gold-silver nanoparticles at the polarized water/1,2-dichloroethane interface using the nonlinear optical technique of surface second-harmonic generation. This study unambiguously demonstrates the excellent stability against aggregation of these core-shell nanoparticles, namely, gold core nanoparticles coated with silver layers of variable thickness, in the presence of an electrolyte salt like lithium chloride. Furthermore, it is also demonstrated that the adsorption of the nanoparticles is reversible by modulating the applied potential at water/1,2-dichloroethane interface. The analysis of these results is performed within the Debye-Huckel approximation of the electrostatic interactions between the nanoparticles. This approach shows that the stability of core-shell nanoparticles can be attributed to the formation of a silver oxide layer at the Surface of the particles.
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| 9. |
- Ablyasova, Olesya S., et al.
(författare)
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Electronic Structure of the Complete Series of Gas-Phase Manganese Acetylacetonates by X-ray Absorption Spectroscopy
- 2023
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 127:34, s. 7121-7131
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Tidskriftsartikel (refereegranskat)abstract
- Metal centers in transition metal–ligand complexes occur in a variety of oxidation states causing their redox activity and therefore making them relevant for applications in physics and chemistry. The electronic state of these complexes can be studied by X-ray absorption spectroscopy, which is, however, due to the complex spectral signature not always straightforward. Here, we study the electronic structure of gas-phase cationic manganese acetylacetonate complexes Mn(acac)1–3+ using X-ray absorption spectroscopy at the metal center and ligand constituents. The spectra are well reproduced by multiconfigurational wave function theory, time-dependent density functional theory as well as parameterized crystal field and charge transfer multiplet simulations. This enables us to get detailed insights into the electronic structure of ground-state Mn(acac)1–3+ and extract empirical parameters such as crystal field strength and exchange coupling from X-ray excitation at both the metal and ligand sites. By comparison to X-ray absorption spectra of neutral, solvated Mn(acac)2,3 complexes, we also show that the effect of coordination on the L3 excitation energy, routinely used to identify oxidation states, can contribute about 40–50% to the observed shift, which for the current study is 1.9 eV per oxidation state.
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| 10. |
- Abou-Hamad, Edy, et al.
(författare)
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Hydrogenation of C-60 in Peapods: Physical Chemistry in Nano Vessels
- 2009
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Ingår i: The Journal of Physical Chemistry C. - WASHINGTON, DC 20036 : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 113:20, s. 8583-8587
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogenation of C-60 molecules inside SWNT was achieved by direct reaction with hydrogen gas at elevated pressure and temperature. Evidence for the C-60 hydrogenation in peapods is provided by isotopic engineering with specific enrichment of encapsulated species and high resolution C-13 and H-1 NMR spectroscopy with the observation of characteristic diamagnetic and paramagnetic shifts of the NMR lines and the appearance of sp(3) carbon resonances. We estimate that approximately 78% of the C-60 molecules inside SWNTs are hydrogenated to an average degree of 14 hydrogen atoms per C-60 molecule. As a consequence, the rotational dynamics of the encapsulated C60Hx molecules is clearly hindered. Our successful hydrogenation experiments open completely new roads to understand and control confined chemical reactions at the nano scale
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