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  • 1.
    Vahlberg, Cecilia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Linares, Mathieu
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Villaume, Sebastien
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Norman, Patrick
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Uvdal, Kajsa
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, The Institute of Technology.
    Noradrenaline and a Thiol Analogue on Gold Surfaces: An Infrared Reflection-Absorption Spectroscopy, X-ray Photoelectron Spectroscopy, and Near-Edge X-ray Absorption Fine Structure Spectroscopy Study2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 1, p. 165-175Article in journal (Refereed)
    Abstract [en]

    Self-assembled monolayers and multilayers of a noradrenaline analogue (Nor-Pt) on gold substrates as well as multilayers of noradrenaline have been investigated by means of the molecular orientation, the molecule surface interaction, the molecular composition and the functional group availability for further biointeraction processes, using X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRAS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. A chemical shift (1.7 eV) of the S 2p peak to lower binding energies is observed, in the XPS spectrum, indicating that the Nor-Pt molecules are chemisorbed onto the gold substrate. The IR results show that Nor-Pt adsorbate has the C=O stretching vibration modes parallel oriented relative to the gold substrate. The average tilt angle of the aromatic ring relative to the gold surface normal is determined to be approximately 51 degrees, based on the NEXAFS measurements on Nor-Pt monolayers. The experimental results and assignments are supported with theoretical studies where we use the building block principle in the spectral analysis and compare with the measurements of noradrenaline and Nor-Pt. The theoretical calculations are shown to be useful; for angle dependence NEXAFS studies as resonances with fully pi* or sigma* character are preferred for correct analysis.

  • 2.
    Villaume, Sebastien
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Ekstrom, Ulf
    Vrije University Amsterdam.
    Ottosson, Henrik
    Uppsala University.
    Norman, Patrick
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Near sulfur L-edge X-ray absorption spectra of methanethiol in isolation and adsorbed on a Au(111) surface: a theoretical study using the four-component static exchange approximation2010In: PHYSICAL CHEMISTRY CHEMICAL PHYSICS, ISSN 1463-9076, Vol. 12, no 21, p. 5596-5604Article in journal (Refereed)
    Abstract [en]

    The relativistic four-component static exchange approach for calculation of near-edge X-ray absorption spectra has been reviewed. Application of the method is made to the Au(111) interface and the adsorption of methanethiol by a study of the near sulfur L-edge spectrum. The binding energies of the sulfur 2p(1/2) and 2p(3/2) sublevels in methanethiol are determined to be split by 1.2 eV due to spin-orbit coupling, and the binding energy of the 2p(3/2) shell is lowered from 169.2 eV for the isolated system to 167.4 and 166.7-166.8 eV for methanethiol in mono-and di-coordinated adsorption sites, respectively (with reference to vacuum). In the near L-edge X-ray absorption fine structure spectrum only the sigma*(S-C) peak at 166 eV remains intact by surface adsorption, whereas transitions of predominantly Rydberg character are largely quenched in the surface spectra. The sigma*(S-H) peak of methanethiol is replaced by low-lying, isolated, sigma*(S-Au) peak(s), where the number of peaks in the latter category and their splittings are characteristic of the local bonding situation of the sulfur.

  • 3.
    Villaume, Sebastien
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics.
    Norman, Patrick
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    On Circular Dichroism and the Separation Between Chromophore and Chiral Center: The Near Carbon K-Edge X-ray Absorption and Circular Dichroism Spectra of Noradrenaline and L-DOPA2009In: Chirality, ISSN 0899-0042, E-ISSN 1520-636X, Vol. 21, no 1E, p. E13-E19Article in journal (Refereed)
    Abstract [en]

    The near carbon K-edge X-ray absorption and circular dichroism spectra of noradrenaline (neutral and protonated forms) and L-DOPA (protonated form) have been determined with use of the complex polarization propagator method in conjunction with Kohn-Sham density functional theory. A Coulomb attenuated exchange-correlation functional and London atomic orbitals have been employed to address the issues of hole-electron interactions and gauge-origin dependence of the magnetic-dipole operator, respectively. Results show that the characteristics of the chromophore part of the circular dichroism spectra are shared for all three considered systems, whereas protonation qualitatively alters the part of the spectrum assigned to the chiral side chain. The comparatively larger spatial separation of chromophore and chiral center in L-DOPA inflicts larger differences in spectral intensities between the chromophore and chiral center part of the circular dichroism spectra.

  • 4.
    Villaume, Sebastien
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Saue, Trond
    Université de Strasbourg.
    Norman, Patrick
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Linear complex polarization propagator in a four-component Kohn-Sham framework2010In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, no 6Article in journal (Refereed)
    Abstract [en]

    An algorithm for the solution of the linear response equation in the random phase approximation is presented. All entities including frequency arguments, matrices, and vectors, are assumed to be complex, and it represents the core equation solver needed in complex polarization propagator approaches where nonstimulated relaxation channels are taken into account. Stability and robustness of the algorithm are demonstrated in applications regarding visible, ultraviolet, and x-ray spectroscopies. An implementation of the algorithm at the level of four-component relativistic, noncollinear, density functional theory for imaginary (but not complex) frequency arguments has been achieved and is used to determine the electric dipole dispersion interaction coefficients for the rubidium and cesium dimers. Our best estimates for the C(6) coefficients of Rb(2) and Cs(2) are equal to 14.0x10(3) and 21.9x10(3) a.u., respectively.

  • 5.
    Zhu, Jun
    et al.
    Uppsala University, Uppsala, Sweden.
    Dahlstrand, Christian
    Uppsala University, Uppsala, Sweden.
    Smith, Joshua R.
    Uppsala University, Uppsala, Sweden; Humboldt State University, Arcata, USA.
    Villaume, Sebastien
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology. Uppsala University, Uppsala, Sweden.
    Ottosson, Henrik
    Uppsala University, Uppsala, Sweden.
    On the Importance of Clar Structures of Polybenzenoid Hydrocarbons as Revealed by the pi-Contribution to the Electron Localization Function2010In: Symmetry, ISSN 2073-8994, E-ISSN 2073-8994, Vol. 2, no 3, p. 1653-1682Article in journal (Refereed)
    Abstract [en]

    The degree of pi-electron (de) localization and aromaticity of a series of polybenzenoid hydrocarbons (PBHs) has been analyzed through the pi-contribution to the electron localization function (ELF pi), calculated at the B3LYP/ 6-311G(d, p) hybrid density functional theory level. The extent of. -electron delocalization in the various hexagons of a PBH was determined through analysis of the bifurcation values of the ELF. basins (BV(ELF.)), the spans in the bifurcation values in each hexagon (BV(ELF pi)), and the ring-closure bifurcation values of the ELF pi (RCBV(ELF pi)). These computed results were compared to the qualitative description of local aromaticities of the different hexagons in terms of Clar structures with pi-sextets. Benzene, [18] annulene, and thirty two PBHs were analyzed at their equilibrium geometries, and benzene and triphenylene were also analyzed at bond length distorted structures. In general, the description of PBHs in terms of Clar valence structures is supported by the ELF pi properties, although there are exceptions. For PBHs at their equilibrium geometries there is a clear sigmoidal relationship between the CC bond lengths and the amount of pi-electron (de) localization at these bonds, however, this relationship is lost for bond distorted geometries. In the latter cases, we specifically examined benzene in D3h symmetric " 1,3,5-cyclohexatriene" structures and triphenylene in eight different structures. From the distorted benzenes and triphenylenes it becomes clear that there is a distinct tendency for the pi-electron network to retain delocalization (aromaticity). The ELF. analysis thus reveals an antidistortive rather than a distortive behavior of the pi-electrons in these investigated compounds.

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