| 1. |
- O'Shea, James N, et al.
(författare)
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Molecular damage in bi-isonicotinic acid adsorbed on rutile TiO2(110)
- 2008
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 602:9, s. 1693-1698
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Tidskriftsartikel (refereegranskat)abstract
- Here we present the characteristic signatures in X-ray absorption and photoemission spectroscopy for molecular damage in adsorbed monolayers of bi-isonicotinic acid on a rutile TiO2(110) surface. Bi-isonicotinic acid is the anchor ligand through which many important inorganic complexes are bound to the surface of TiO2 in dye-sensitized solar cells. The nature of the damage caused by excessive heating of the adsorbed monolayer is consistent with splitting the molecule into two adsorbed isonicotinic acid molecular fragments. The effect on the lowest unoccupied molecular orbitals (involved in electron transfer in the molecule) can be understood in terms of the adsorption geometry of the reaction products and their nearest neighbor interactions.
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| 2. |
- O'Shea, James N., et al.
(författare)
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Ultra-fast intramolecular vibronic coupling revealed by RIXS and RPES maps of an aromatic adsorbate on TiO2(110)
- 2018
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 148:20
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional resonant inelastic x-ray scattering (RIXS) and resonant photoelectron spectroscopy (RPES) maps are presented for multilayer and monolayer coverages of an aromatic molecule (bi-isonicotinic acid) on the rutile TiO2(110) single crystal surface. The data reveal ultra-fast intramolecular vibronic coupling upon core excitation from the N 1s orbital into the lowest unoccupied molecular orbital (LUMO) derived resonance. In the RIXS measurements, this results in the splitting of the participator decay channel into a purely elastic line which disperses linearly with excitation energy and a vibronic coupling channel at constant emission energy. In the RPES measurements, the vibronic coupling results in a linear shift in binding energy of the participator channel as the excitation is tuned over the LUMO-derived resonance. Localisation of the vibrations on the molecule on the femtosecond time scale results in predominantly inelastic scattering from the core-excited state in both the physisorbed multilayer and the chemisorbed monolayer.
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| 3. |
- Taylor, John B., et al.
(författare)
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Charge transfer dynamics at model metal-organic solar cell surfaces
- 2007
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:44, s. 16646-16655
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Tidskriftsartikel (refereegranskat)abstract
- The "core-hole clock" implementation of resonant photoemission has been used to investigate the charge-transfer dynamics of bi-isonicotinic acid molecules (4,4'-dicarboxy-2,2'-bipyridine) adsorbed on a rutile TiO2(110) surface containing varying densities of gold islands. In the presence of, nominally, a few monolayers of gold there exists a strong coupling between the adsorbed molecules and the surface. This is derived from the measurement of a <3 fs charge-transfer time for the injection of a core-excited electron into the substrate. This ultrafast charge-transfer time is quenched for a fraction of the molecules upon the addition of only a few further monolayers of gold. There is evidence to suggest that this effect derives from a change in the bonding configuration of bi-isonicotinic acid molecules. However, results also support the occurrence of ultrafast back-transfer from Au states to core-excited unoccupied molecular states.
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| 4. |
- Taylor, John B., et al.
(författare)
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The adsorption and charge transfer dynamics of bi-isonicotinic acid on Au(111)
- 2007
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127:13
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of bi-isonicotinic acid (4,4[prime]-dicarboxy-2,2[prime]-bipyridine) with the Au(111) surface has been investigated using electron spectroscopic techniques. Near edge x-ray absorption fine structure (NEXAFS) spectra show that monolayers of the molecule lie flat to the surface and also reveal that the monolayer is sensitive to the preparation conditions employed. Core level x-ray photoelectron spectroscopy (XPS) shows that the adsorbed molecule does not undergo deprotonation upon adsorption. The “core-hole clock” implementation of resonant photoemission has been used to probe the coupling between molecule and substrate. This technique has revealed the possibility of ultrafast backtransfer from the substrate into the molecule upon resonant excitation of a N 1s core level electron. This is supported by a NEXAFS and XPS investigation of energy level alignments in the system. ©2007 American Institute of Physics
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| 5. |
- Swarbrick, Janine C., et al.
(författare)
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Electronic structure changes in cobalt phthalocyanine due to nanotube encapsulation probed using resonant inelastic X-ray scattering
- 2010
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 12:33, s. 9693-9699
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of cobalt phthalocyanine (CoPc) changes upon encapsulation inside multi-walled carbon nanotubes (CoPc@MWNT), as detected in this research using Co-K-edge X-ray absorption near-edge structure spectroscopy (XANES) and Co-K alpha(1) resonant inelastic X-ray scattering (RIXS). The CoPc molecules are no longer planar once inside the nanotubes, and the molecular symmetry is found to change upon encapsulation from D-4h to C-4v symmetry. This change of symmetry increases the amount of p-d orbital mixing, which is seen in the spectra as a change in peak intensity. Energy shifts are also seen between CoPc and CoPc@MWNT, showing that Co in the encapsulated species is more oxidized due to electron donation from the phthalocyanine molecule to the surrounding nanotube. Trends seen in the spectra between CoPc and CoPc@MWNT can be calculated using density functional theory (DFT), which shows the molecular orbitals involved in different spectral features.
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| 6. |
- Swarbrick, Janine C, et al.
(författare)
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High energy resolution X-ray absorption spectroscopy of environmentally relevant lead(II) compounds
- 2009
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Ingår i: Inorganic chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 48:22, s. 10748-10756
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Tidskriftsartikel (refereegranskat)abstract
- The determination of the chemical environment of Pb in natural samples is a challenge of great importance in environmental and health physics. We report a high energy resolution fluorescence detection (HERFD) X-ray absorption near-edge spectroscopy (XANES) study at the Pb L(3) and L(1) absorption edges to determine the chemical environment of Pb in a series of model and environmentally relevant compounds. HERFD spectroscopy can reveal increased spectral detail due to an apparent reduction in the core hole lifetime broadening. HERFD spectra of model Pb(II) compounds were compared to FEFF 8.4 multiple scattering calculations with reduced peak broadening parameters, and density of state (DOS) simulations, to determine the origins of the spectral features. A pre-edge in the L(3) XANES is revealed which is shown to arise from hybridization between the Pb p and d states. HERFD spectra of Pb(II)-containing environmentally relevant solutions were compared to model spectra and calculations. The results presented in this paper show that the chemical environment of Pb can be identified from spectral features resolved in HERFD spectroscopy at the Pb L(3) edge. The technique provides information that is complementary to conventional extended X-ray absorption fine structure (EXAFS) spectroscopy.
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| 7. |
- Swarbrick, Janine C., et al.
(författare)
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Ligand Identification in Titanium Complexes Using X-ray Valence-to-Core Emission Spectroscopy
- 2010
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 49:18, s. 8323-8332
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Tidskriftsartikel (refereegranskat)abstract
- The identification of ligands in metalloorganic complexes is crucial for understanding many important biological and chemical systems. Nonresonant K beta valence-to-core X-ray emission spectroscopy (XES) has been demonstrated as a ligand identification technique which is complementary to other spectroscopies, such as X-ray absorption. In this study we show the K beta valence-to-core XES alongside the Ti K-edge X-ray absorption near edge structure spectra for a series of chemically relevant low-symmetry Ti organometallic complexes. The spectra are modeled using density functional theory calculations. XES spectra are analyzed in terms of the molecular orbitals probed, in order to understand the effects of bond length, bond nature, orbital hybridization, and molecular symmetry on the observed spectral features.
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