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  • 1.
    Fredriksson, Andreas
    et al.
    Luleå University of Technology.
    Hellström, Pär
    Luleå University of Technology.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Comparison between in situ total internal reflection vibrational spectroscopy of an adsorbed collector and spectra calculated by ab initio density functional theory methods2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 26, p. 9299-9304Article in journal (Refereed)
    Abstract [en]

    In this investigation, adsorbed heptyl xanthate on a Ge(111) surface was studied, as well as the free heptyl xanthate molecule, by means of first-principle density functional theory calculations. The modeled results were compared with the in situ total internal reflection vibrational spectroscopy spectra of heptyl xanthate adsorbed on a germanium internal reflection element and the transmission infrared spectrum of a heptyl xanthate ion in aqueous solution. The assignments of the vibrational frequencies were done for the adsorbed xanthate. The region between 1150 and 1000 cm(-1) seems suitable for discussing differences between an adsorbed xanthate and its corresponding ion. The modeled spectra for both the adsorbed xanthate and the xanthate ion are in good agreement with the experimentally retrieved spectra. This investigation shows the strength of using DFT calculations in the interpretation of absorption bands from molecules adsorbed at surfaces in situ.

  • 2.
    Hellström, Pär
    Luleå University of Technology.
    Ab initio modeling of xanthate adsorption on ZnS surfaces2005Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Modeling surface adsorption requires systems of hundreds of atoms. To model such systems at an ab initio level successfully, we need to avoid traditional quantum chemical methods. In the present work we have shown that density functional theory is a powerful modeling tool for large chemical systems especially in combinations with pseudopotentials This is validated by an initial study of ethyl and heptyl xanthates and their sodium/potassium salts. In this study, all electron calculations using both Hartree-Fock and density functional theory methods are compared with experimental infrared results. To do this the influence of basis sets and modeling approaches on the geometrical structure and the vibrational modes are examined. This includes comparing the pseudopotential and full electron potential approaches. Results obtained from pseudopotential methods are in close agreement with both all electron calculations as well as experimental results, here used to study adsorption of heptyl xanthate ZnS surfaces. Vibrational frequencies of the adsorbed species is presented, together with calculations of the tilt angles. The investigation of the tilt angles resulted in 20.3° 20.6° and 25.2° for the 100, 110 and 111 surfaces respectively. Heptyl xanthate forms a bridging confirmation on both the 110 and 111 surfaces and a bidentate confirmation on the 100 surface. Assignments of vibrational modes of ethyl/heptyl xanthate molecule and its corresponding potassium/sodium salts are also reported.

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  • 3.
    Hellström, Pär
    et al.
    Luleå University of Technology.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    An ab initio study of ethyl xanthate adsorbed on Ge(111) surfaces2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 45, p. 16920-16926Article in journal (Refereed)
    Abstract [en]

    The interaction between adsorbed ethyl xanthate on a clean Ge(111) surface and a hydroxylated surface was studied, using first-principle density functional theory. Geometrically optimized structures are presented and discussed. Results suggest a bidentate bridging conformation on a clean Ge(111) surface, whereas a monodentate bonding is preferred when the surface is saturated by hydrogen atoms. Then the interaction with a hydroxylated surface was considered. The lowest energy configuration was obtained when xanthate binds with one sulfur to the surface and with the other to an OH group adsorbed on the surface. A marker for this configuration was found in the vibrational spectra at 3200 cm-1. Vibrational frequencies down to 250 cm-1 were calculated and assigned to vibrational modes and presented together with the calculated infrared spectra. The tilt angle of the hydrocarbon chain was also investigated.

  • 4.
    Hellström, Pär
    et al.
    Luleå University of Technology.
    Larsson, Anna-Carin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Fredriksson, Andreas
    Luleå University of Technology.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Study of potassium O,O′-dibutyldithiophosphate combining DFT, 31P CP/MAS NMR and infrared spectroscopy2008In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 112, no 46, p. 11777-11783Article in journal (Refereed)
    Abstract [en]

    Dithiophosphates are used in many different industrial applications. To explain their functions and properties in these applications, a fundamental understanding on a molecular level is needed. Potassium O,O′-Dibutyldithiophosphate and its anion have been investigated by means of a combination of DFT and 31P CP/MAS NMR and infrared spectroscopy. Several low-energy conformations were studied by DFT. Three different conformations with significantly different torsion angles of the O-C bond relative to the O-P-O plane were selected for further studies of infrared frequencies and 31P NMR chemical-shift tensors. A good agreement between theoretical and experimental results was obtained, especially when the IR spectra or 31P chemical shift tensor parameters of all three conformations were added, indicating that, because of the low energy difference between the conformations, the molecules are rapidly fluctuating between them.

  • 5.
    Hellström, Pär
    et al.
    Luleå University of Technology.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Fredriksson, Andreas
    Luleå University of Technology.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    A theoretical and experimental study of vibrational properties of alkyl xanthates2006In: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy, ISSN 1386-1425, E-ISSN 1873-3557, Vol. 65, no 3-4, p. 887-895Article in journal (Refereed)
    Abstract [en]

    Geometrical structure and vibrational modes of potassium and sodium ethyl/heptyl xanthates were studied, using both theoretical and experimental methods. Both Hartree-Fock and density functional theory were used. The experimental method used was infrared absorption spectroscopy (FTIR). Our work showed that vibrational frequencies calculated with density functional theory, using the local density approximation, are in very good agreement with experiments. The results were not improved by using the more sophisticated and computationally demanding B3LYP functional.

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