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  • 1.
    Billes, Ferenc
    et al.
    Department of Physical Chemistry, Budapest University of Technology and Economics, Budapest.
    Mohammed-Ziegler, Ildikó
    Institute of Chemistry, Chemical Research Center, Hungarian Academy of Sciences, Budapest.
    Mikosch, Hans
    Institute for Solid State Chemistry and Electrochemistry, Vienna University of Technology.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Vibrational spectroscopic and conformational analysis of pinosylvin2002In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 106, no 26, p. 6232-6241Article in journal (Refereed)
    Abstract [en]

    Infrared and Raman spectra of pinosylvin were recorded and the vibrational frequencies with the corresponding infrared intensities were compared with the results of ab initio calculations utilizing the DFT method with the Becke3P86 functional and the 6-31G(d) basis set. Normal coordinate analysis was carried out. The effect of the conformation of the OH groups on the distribution of net charges, molecular energy and vibrational fundamentals were analyzed. One of the OH-cis-OH-trans conformers has the lowest energy. The conformation has a strong effect on the aforementioned properties, e.g., the cis-to-trans transition generates electron repulsion toward the vinylidene group between the two benzene rings. The changes in the different properties are in good accordance with each other. For comparison, the vibrational spectra were also recorded and calculated for the parent compound, trans-stilbene.

  • 2.
    Golubev, Nikolay V.
    et al.
    Department of Chemistry, M. V. Lomonosov Moscow State University.
    Bezrukov, Dmitry S.
    Department of Chemistry, M. V. Lomonosov Moscow State University.
    Gustafsson, Magnus
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Nyman, Gunnar
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Antipov, Sergey V.
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Formation of the SiP radical through radiative association2013In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 117, no 34, p. 8184-8188Article in journal (Refereed)
    Abstract [en]

    Formation of the SiP radical through radiative association of Si( 3P) and P(4S) atoms is studied using classical and quantum dynamics. Rate coefficients for formation in the two lowest doublet states and the two lowest quartet states are calculated for T = 10-20 000 K. Breit-Wigner theory is used to properly account for contribution from quantum mechanical resonances.

  • 3.
    Larsson, Anna-Carin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Hellström, Pär
    Fredriksson, Andreas
    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.

  • 4.
    Larsson, Anna-Carin
    et al.
    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 on potassium iso-propylxanthate and its decomposition products: experimental 13C CP/MAS NMR combined with DFT calculations2011In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 115, no 8, p. 1396-1407Article in journal (Refereed)
  • 5.
    Malysheva, Lyuba
    et al.
    Bogolyubov Institute for Theoretical Physics, Kiev.
    Onipko, Alexander
    Valiokas, Ramunas
    Department of Physics, Chemistry and Biology, Linköping University.
    Liedberg, Bo
    Department of Physics, Chemistry and Biology, Linköping University.
    Molecular orientation in helical and all-trans oligo(ethylene glycol)-terminated assemblies on gold: results of ab initio modeling2005In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 109, no 34, p. 7788-7796Article in journal (Refereed)
    Abstract [en]

    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.

  • 6.
    Muthukumar, Kaliappan
    et al.
    Tyndall National Institute, University College Cork.
    Larsson, Andreas
    A density functional study of Ce@C82: Explanation of the Ce preferential bonding site2008In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 112, no 5, p. 1071-1075Article in journal (Refereed)
    Abstract [en]

    Ce has been found experimentally to be preferentially incorporated into the C82 isomer of C2v symmetry as have other lanthanoids in M@C82 (M = La, Pr, Nd, etc.). We have investigated the underlying reason for this preference by calculating structural and electronic properties of Ce@C82 using density functional theory. The ground-state structure of Ce@C82 is found to have the cerium atom attached to the six-membered ring on the C2 axis of the C82-C2v cage, and the encapsulated atom is found to perturb the carbon cage due to chemical bonding. We have found Ce to favor this C2v chemisorption site in Cv2 by 0.62 eV compared to other positions on the inside wall of the cage. The specific preference of the metal atom to this six-membered ring is explained through electronic structure analysis, which reveals strong hybridization between the d orbitals of cerium and the π orbitals of the cage that is particularly favorable for this chemisorption site. We propose that this symmetry dictated interaction between the cage and the lanthanide d orbital plays a crucial role when C82 forms in the presence of Ce to produce Ce@C82 and is also more generally applicable for the formation of other lanthanoid M@C82 molecules. Our theoretical computations are the first to explain this well-established fact. Last, the vibrational spectrum of Ce@C82 has been simulated and analyzed to gain insight into the metal-cage vibrations

  • 7.
    Persson, Ingmar
    et al.
    Department of Molecular Sciences, Swedish University of Agricultural Sciences.
    Trublet, Mylene
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Klysubun, Wantana
    Synchrotron Light Research Institute.
    Structure Determination of Phosphoric Acid and Phosphate Ions in Aqueous Solution Using EXAFS Spectroscopy and Large Angle X-ray Scattering2018In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 122, no 37, p. 7413-7420Article in journal (Refereed)
    Abstract [en]

    The structures of hydrated phosphoric acid and phosphate ions (H2PO4-, HPO42- and PO43-) in aqueous solution have been determined by P K-edge EXAFS and large angle X-ray scattering (LAXS). The P-O bond distance in all phosphate species studied is close to 1.53 Å. The P-(O)⋅⋅⋅Oaq distances have been refined to ca. 3.6 Å from the LAXS data giving a P-O⋅⋅⋅Oaq bond angle close to tetrahedral suggesting that each oxygen or OH group of phosphoric acid and dihydrogenphosphate, on average, hydrogen bind three water molecules. The (P-)O(-H)···Oaq and (P-)O···(H-)Oaq hydrogen bonds in hydrated phos-phoric acid and the H2PO4- ion are shorter than the hydrogen bonds in neat water. This supports previous infrared spectro-scopic studies claiming that the hydrogen bonds in hydrated phosphoric acid and phosphate ions are stronger than the hy-drogen bonds in neat water. Phosphoric acid and phosphate ions can therefore be regarded as structure making solutes. This is the first study applying transmission mode X-ray absorption spectroscopy (XAS) data collection on the P K-edge. It shows that XAS spectra collected in transmission mode have a much better S/N ratio than data collected in fluorescence mode, allowing accurate determination of P-O bond distances. Furthermore, P K-edge EXAFS data collected in fluorescence mode display a higher amplitude at high k than expected due to increasing radiated volume of the sample with increasing energy as the total absorption decreases sharply with increasing energy of the X-rays. As a result, the fluorescence signal becomes non-proportional to the intensity of the X-ray beam over the EXAFS spectrum. This results in an increasing amplitude of the EXAFS function with increasing energy of the X-ray beam resulting in too small Debye-Waller coefficients.

  • 8.
    Roukala, Juho
    et al.
    NMR Research Unit, University of Oulu .
    Orr, Simon T.
    Department of Physics, The University of Warwick.
    Hanna, John V.
    Department of Physics, The University of Warwick.
    Vaara, Juha
    NMR Research Unit, University of Oulu .
    Ivanov, Alexander V.
    Institute of Geology and Nature Management, Far Eastern Branch of the Russian Academy of Sciences .
    Antzutkin, Oleg
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Lantto, Perttu
    NMR Research Unit, University of Oulu .
    Experimental and First-Principles NMR Analysis of Pt(II) Complexes With O,O'-Dialkyldithiophosphate Ligands2016In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 120, no 42, p. 8326-8338Article in journal (Refereed)
    Abstract [en]

    Polycrystalline bis(dialkyldithiophosphato)Pt(II) complexes of the form [Pt{S2P(OR)2}2] (R = ethyl, iso-propyl, iso-butyl, sec-butyl or cyclo-hexyl group) were studied using solid-state 31P and 195Pt NMR spectroscopy, to determine the influence of R to the structure of the central chromophore. The measured anisotropic chemical shift (CS) parameters for 31P and 195Pt afford more detailed chemical and structural information, as compared to isotropic CS and J couplings alone. Advanced theoretical modeling at the hybrid DFT level, including both crystal lattice and the important relativistic spin-orbit effects qualitatively reproduced the measured CS tensors, supported the experimental analysis, and provided extensive orientational information. A particular correction model for the non-negligible lattice effects was adopted, allowing one to avoid a severe deterioration of the 195Pt anisotropic parameters due to the high requirements posed on the pseudopotential quality in such calculations. Though negligible differences were found between the 195Pt CS tensors with different substituents R, the 31P CS parameters differed significantly between the complexes, implying the potential to distinguish between them. The presented approach enables good resolution and a detailed analysis of heavy-element compounds by solid-state NMR, thus widening the understanding of such systems.

  • 9.
    Svensson, Karl-Mikael
    et al.
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Gustafsson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Nyman, Gunnar
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Formation of the Hydroxyl Radical by Radiative Association2015In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 119, no 50, p. 12263-12269Article in journal (Refereed)
    Abstract [en]

    The reaction rate constant for the radiative association of O(3P) and H(2S) has been calculated by combining a few different methods and taking account of both direct and resonance-mediated pathways. The latter includes both shape resonances and Feshbach type inverse predissociation. The reaction rate constant is expressed as a function of temperature in the interval 10−30000 K. This reaction may be astrochemically relevant and is expected to be of use in astrochemical networks.

  • 10.
    Szabo, Peter
    et al.
    Department of General and Inorganic Chemistry, Institute of Chemistry, University of Pannonia.
    Lendvay, György
    Department of General and Inorganic Chemistry, Institute of Chemistry, University of Pannonia.
    A Quasiclassical Trajectory Study of the Reaction of H Atoms with O2(1Δg)2015In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 119, no 28, p. 7180-7189Article in journal (Refereed)
    Abstract [en]

    The kinetic and dynamic characteristics of the reaction of H atoms with electronically excited O2 were studied using the quasiclassical trajectory (QCT) method and the potential energy surface of Li et al. (J. Chem. Phys. 2010, 133, 144306−144314). The reaction takes place via a deep potential well that can be entered by climbing a barrier in the reactant valley and can be left without a barrier on the product side. In this reaction, the basic assumptions of statistical rate theories are not fulfilled: (i) 80% of the trajectories cross the barrier region twice and are nonreactive; (ii) the energy is not equilibrated in the HO2 potential well. The QCT cross sections agree well with those from the existing exact quantum-mechanical data and extend them to vib-rotationally excited reactants. The thermal rate coefficients agree well with measurements of pure reactive quenching of O2(1Δg) and are lower than those involving both reactive and electronic quenching. The temperature dependence is described as k2 = 5.81 × 10–16 T1.45 exp(−2270/T) cm3 molecule–1 s–1. On the basis of a comparison of the QCT data with the two kinds of experiments, we estimate that electronic quenching is faster than reaction by a factor of about 10 at low and 2 at high flame temperatures.

  • 11.
    Szabo, Peter
    et al.
    Department of General and Inorganic Chemistry, Institute of Chemistry, University of Pannonia.
    Lendvay, György
    Department of General and Inorganic Chemistry, Institute of Chemistry, University of Pannonia.
    Dynamics of Complex-Forming Bimolecular Reactions: A Comparative Theoretical Study of the Reactions of H Atoms with O2(3Σg–) and O2(1Δg)2015In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 119, no 50, p. 12485-12497Article in journal (Refereed)
    Abstract [en]

    The atomic-level mechanism of the reaction of H atoms with triplet and singlet molecular oxygen, H(2S) + O2(3Σg–) → O(3P) + OH(2Πg) (R1) and H(2S) + O2(1Δg) → O(3P) + OH(2Πg) (R2) is analyzed in terms of the topology of the potential energy surfaces (PES) of the two reactions. Both PES exhibit a deep potential well corresponding to the ground and first excited electronic state of HO2. The ground-state reaction is endothermic with no barrier on either side of the well; the excited-state reaction is exothermic with a barrier in the entrance valley of the PES. The differences of the PES are manifested in properties such as the excitation functions, which show reaction R1 to be much slower and the effect of rotational excitation on reactivity, which speeds up reaction R1 and has little effect on R2. Numerous common dynamics features arise from the presence of the deep potential well on the PES. Such are the significant role of isomerization (for example, 90% of reactive collisions in R2 involve at least one H atom transfer from one of the O atoms to the other in reaction R2), which is shown to give rise to a significant rotational excitation of the product OH radicals. Common is the significant sideways scattering of the products that originates from collisions in propeller-type arrangements induced by the presence of two bands of acceptance around the O2 molecule. The HO2 complex in both reactions proves to behave nonstatistically, with signatures of the dynamics in lifetime distributions, angular distributions, opacity functions, and product quantum-state distributions.

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