Knut J Børve

Publications of Knut J Børve

• Structure of neutral nanosized clusters produced by coexpansion of CF4 and CH4.

  Authors: M Winkler, J Harnes, K J Børve

  The journal of physical chemistry. A. 09/2011; 115(46):13259-68.

  Mixed CH(4)/CF(4) clusters as well as pure clusters of CF(4) were produced by adiabatic expansion and studied by carbon 1s (C1s) X-ray photoelectron spectroscopy. Evidence is presented that CH(4) andMixed CH(4)/CF(4) clusters as well as pure clusters of CF(4) were produced by adiabatic expansion and studied by carbon 1s (C1s) X-ray photoelectron spectroscopy. Evidence is presented that CH(4) and CF(4) do indeed form binary clusters in CH(4)/CF(4) coexpansion experiments and that these clusters exhibit radial structure; i.e., CF(4) is primarily found in the bulk. The interpretation of the photoelectron spectra is supported by calculations of C1s ionization energies based on theoretical clusters models.

• Size of free neutral CO2 clusters from carbon 1s ionization energies.

  Authors: J Harnes, M Winkler, A Lindblad, L J Sæthre, K J Børve

  The journal of physical chemistry. A. 08/2011; 115(38):10408-15.

  Free neutral CO(2) clusters were produced by adiabatic expansion and characterized by carbon 1s (C1s) photoelectron spectroscopy using synchrotron radiation. The shift in C1s ionization energy (IE)Free neutral CO(2) clusters were produced by adiabatic expansion and characterized by carbon 1s (C1s) photoelectron spectroscopy using synchrotron radiation. The shift in C1s ionization energy (IE) between the cluster and the monomer, i.e., ΔIE = IE(cluster) - IE(monomer), was found to vary systematically with the experimental conditions. A functional relationship is established between the mean cluster size in the beam, , and ΔIE, in good agreement with theoretical calculations of shifts in ionization energy for model clusters. This makes it possible to use core-level photoelectron spectroscopy to monitor the mean cluster size and also to estimate from expansion conditions.

• On the origins of core-electron chemical shifts of small biomolecules in aqueous solution: insights from photoemission and ab initio calculations of glycine(aq).

  Authors: Niklas Ottosson, Knut J Børve, Daniel Spångberg, Henrik Bergersen, Leif J Sæthre, Manfred Faubel, Wandared Pokapanich, Gunnar Öhrwall, Olle Björneholm, Bernd Winter

  Journal of the American Chemical Society. 02/2011; 133(9):3120-30.

  The local electronic structure of glycine in neutral, basic, and acidic aqueous solution is studied experimentally by X-ray photoelectron spectroscopy and theoretically by molecular dynamicsThe local electronic structure of glycine in neutral, basic, and acidic aqueous solution is studied experimentally by X-ray photoelectron spectroscopy and theoretically by molecular dynamics simulations accompanied by first-principle electronic structure and spectrum calculations. Measured and computed nitrogen and carbon 1s binding energies are assigned to different local atomic environments, which are shown to be sensitive to the protonation/deprotonation of the amino and carboxyl functional groups at different pH values. We report the first accurate computation of core-level chemical shifts of an aqueous solute in various protonation states and explicitly show how the distributions of photoelectron binding energies (core-level peak widths) are related to the details of the hydrogen bond configurations, i.e. the geometries of the water solvation shell and the associated electronic screening. The comparison between the experiments and calculations further enables the separation of protonation-induced (covalent) and solvent-induced (electrostatic) screening contributions to the chemical shifts in the aqueous phase. The present core-level line shape analysis facilitates an accurate interpretation of photoelectron spectra from larger biomolecular solutes than glycine.

• Additivity of Substituent Effects. Core-Ionization Energies and Substituent Effects in Fluoromethylbenzenes.

  Authors: Thomas X Carroll, T Darrah Thomas, Leif J Sæthre, Knut J Børve

  The journal of physical chemistry. A. 05/2009; 113(15):3481-3490.

  Carbon 1s ionization energies have been measured for all of the carbon atoms in eight fluoromethylbenzenes. Enthalpies of protonation have been calculated for protonation at all of the ring carbonsCarbon 1s ionization energies have been measured for all of the carbon atoms in eight fluoromethylbenzenes. Enthalpies of protonation have been calculated for protonation at all of the ring carbons in the same molecules. These data together with previously reported data on fluorobenzenes and methylbenzenes provide the basis for studying the additivity of substituent effects and the correlation between enthalpies of protonation with core-ionization energies. Although a linear additivity model accounts reasonably well for both the ionization energies and the enthalpies of protonation, a better description, especially for the enthalpies, is obtained by inclusion of nonlinear terms that account for interactions between two substituents on the same molecule. There are families of nearly parallel correlation lines between enthalpies of protonation and core-ionization energies. The existence of several families can be primarily understood in terms of the linear additivity picture and more completely understood when the nonlinear terms are taken into account. The role of the methyl group as a polarizible pi-electron donor is contrasted with the role of fluorine, which is a substituent of low polarizibility that acts to withdraw electrons from the adjacent carbon and to donate electrons through resonance to the ring. The role of the hydrogen atoms as pi-electron acceptors in the protonated species is illustrated.

• The substituent effect of the methyl group. Carbon 1s ionization energies, proton affinities, and reactivities of the methylbenzenes.

  Authors: Velaug Myrseth, Leif J Saethre, Knut J Børve, T Darrah Thomas

  The Journal of organic chemistry. 08/2007; 72(15):5715-23.

  High-resolution carbon 1s photoelectron spectra have been measured for methyl-substituted benzenes. By using these data together with molecular structure calculations to predict the vibrationalHigh-resolution carbon 1s photoelectron spectra have been measured for methyl-substituted benzenes. By using these data together with molecular structure calculations to predict the vibrational profiles expected in the spectra, it has been possible for the first time to assign 1s ionization energies to each of the inequivalent carbon atoms in these molecules. There exist linear correlations between the ionization energies and the energy changes for other chemical processes, such as enthalpies of protonation and activation energies for hydrogen exchange and protodesilylation. There are deviations from these correlations for sites in which hyperconjugation plays a role in the process. These can be understood by recognizing that the core-ionization energies reflect primarily the Hammett parameter sigma whereas the other energies reflect sigma+. The ionization and reaction energies can be summarized compactly with a linear model in which the total effect of the substituents is equal to the sum of the effects of the individual substituents. A slightly better description is obtained with a quadratic model, which allows for interaction between the substituents.

• Activity of rhodium-catalyzed hydroformylation: added insight and predictions from theory.

  Authors: Manuel Sparta, Knut J Børve, Vidar R Jensen

  Journal of the American Chemical Society. 08/2007; 129(27):8487-99.

  We have performed a density functional theory investigation of hydroformylation of ethylene for monosubstituted rhodium-carbonyl catalysts, HRh(CO)3L, where the modifying ligand, L, is a phosphite (LWe have performed a density functional theory investigation of hydroformylation of ethylene for monosubstituted rhodium-carbonyl catalysts, HRh(CO)3L, where the modifying ligand, L, is a phosphite (L = P(OMe)3, P(OPh)3, or P(OCH2CF3)3), a phosphine (L = PMe3, PEt3, PiPr3, or PPh3), or a N-heterocyclic carbene (NHC) based on the tetrahydropyrimidine, imidazol, or tetrazol ring, respectively. The study follows the Heck and Breslow mechanism. Excellent correspondence between our calculations and existing experimental information is found, and the present results constitute the first example of a realistic quantum chemical description of the catalytic cycle of hydroformylation using ligand-modified rhodium carbonyl catalysts. This description explains the mechanistic and kinetic basis of the contemporary understanding of this class of reaction and offers unprecedented insight into the electronic and steric factors governing catalytic activity. The insight has been turned into structure-activity relationships and used as guidelines when also subjecting to calculation phosphite and NHC complexes that have yet to be reported experimentally. The latter calculations illustrate that it is possible to increase the electron-withdrawing capacity of both phosphite and NHC ligands compared to contemporary ligands through directed substitution. Rhodium complexes of such very electron-withdrawing ligands are predicted to be more active than contemporary catalysts for hydroformylation.

• Structure and stability of networked metallofullerenes of the transition metals.

  Authors: Manuel Sparta, Knut J Børve, Vidar R Jensen

  The journal of physical chemistry. A. 11/2006; 110(41):11711-6.

  A DFT investigation of substitutionally doped fullerenes MC59 of second- and third-row transition metals shows that their stability increases toward the right-hand side of the d-block. Whereas theA DFT investigation of substitutionally doped fullerenes MC59 of second- and third-row transition metals shows that their stability increases toward the right-hand side of the d-block. Whereas the structural deviation from that of C60 depends on the size of the metal atom, stability is governed by electronic properties of the transition metal atom. A range of MC59 compounds of group 6-8 metals are predicted to have sufficient stability for experimental observation.

• Fluorine as a pi donor. Carbon 1s photoelectron spectroscopy and proton affinities of fluorobenzenes.

  Authors: Thomas X Carroll, T Darrah Thomas, Henrik Bergersen, Knut J Børve, Leif J Saethre

  The Journal of organic chemistry. 04/2006; 71(5):1961-8.

  The carbon 1s ionization energies for all of the carbon atoms in 10 fluorine-substituted benzene molecules have been measured by high-resolution photoelectron spectroscopy. A total of 30 ionizationThe carbon 1s ionization energies for all of the carbon atoms in 10 fluorine-substituted benzene molecules have been measured by high-resolution photoelectron spectroscopy. A total of 30 ionization energies can be accurately described by an additivity model with four parameters that describe the effect of a fluorine that is ipso, ortho, meta, or para to the site of ionization. A similar additivity relationship describes the enthalpies of protonation. The additivity parameters reflect the role of fluorine as an electron-withdrawing group and as a pi-electron donating group. The ionization energies and proton affinities correlate linearly, but there are four different correlations depending on whether there are 0, 1, 2, or 3 fluorines ortho or para to the site of ionization or protonation. That there are four correlation lines can be understood in terms of the ability of the hydrogens at the site of protonation to act as a pi-electron acceptor. A comparison of the ionization energies and proton affinities, together with the results of electronic structure calculations, gives insight into the effects of fluorine as an electron-withdrawing group and as a pi donor, both in the neutral molecule and in response to an added positive charge.

• Reactivity and core-ionization energies in conjugated dienes. Carbon 1s photoelectron spectroscopy of 1,3-pentadiene.

  Authors: T Darrah Thomas, Leif J Saethre, Knut J Børve, Maria Gundersen, Edwin Kukk

  The journal of physical chemistry. A. 07/2005; 109(23):5085-92.

  The high-resolution carbon 1s photoelectron spectrum of trans-1,3-pentadiene has been resolved into contributions from the five inequivalent carbon atoms, and carbon 1s ionization energies have beenThe high-resolution carbon 1s photoelectron spectrum of trans-1,3-pentadiene has been resolved into contributions from the five inequivalent carbon atoms, and carbon 1s ionization energies have been assigned to each of these atoms. Spectra have also been measured for propene and 1,3-butadiene at better resolution than has previously been available. The ionization energies for the sp2 carbons are found to correlate well with activation energies for electrophilic addition and with proton affinities. Comparing the results for 1,3-pentadiene with those for ethene, propene, and 1,3-butadiene as well as with results of theoretical calculations makes it is possible to assess the effect of the terminal methyl group in 1,3-pentadiene. As in propene, the methyl group contributes electrons to the beta carbon through the pi system. In addition, there is a significant (though smaller) contribution from the methyl group to the terminal (delta) CH2 carbon, also through the pi system. Most of the effect of the methyl group is present in the ground-state molecule. There are only relatively small contributions from the methyl group to the ionization energies from redistribution of charge in the pi system in response to the removal of a core electron. In addition to these specific effects, there is an overall decrease in average ionization energy as the size of the molecule increases as well as effects that are specific to the conjugated systems in 1,3-butadiene and 1,3-pentadiene. The results provide insight into the reactivity and regioselectivity of conjugated dienes.

• Toward the spectrum of free polyethylene: linear alkanes studied by carbon 1s photoelectron spectroscopy and theory.

  Authors: Tor Karlsen, Knut J Børve, Leif J Saethre, Karoline Wiesner, Margit Bässler, Svante Svensson

  Journal of the American Chemical Society. 08/2002; 124(26):7866-73.

  Trends in carbon 1s ionization energies for the linear alkanes have been investigated using third-generation synchrotron radiation. The study comprises CH(4), C(2)H(6), C(3)H(8), C(4)H(10),Trends in carbon 1s ionization energies for the linear alkanes have been investigated using third-generation synchrotron radiation. The study comprises CH(4), C(2)H(6), C(3)H(8), C(4)H(10), C(5)H(12), C(6)H(14), and C(8)H(18). Both inter- and intramolecular shifts in ionization energy have been determined from gas-phase spectra and ab initio calculations. The shifts are decomposed into initial-state and final-state contributions and are shown to relate to the fundamental chemical properties of group electronegativity and polarizability. By extrapolation, we predict C1s spectra of larger n-alkanes, converging toward isolated strands of polyethylene.

• Reduction of chromium in ethylene polymerisation using bis(imido)chromium(VI) catalyst precursors.

  Authors: Vidar R Jensen, Knut J Børve

  Chemical communications (Cambridge, England). 04/2002;

  Hybrid density functional calculations on [Cr(NR)2C3H7(C2H4)]+ (R = H, tBu) have revealed a facile reductive elimination reaction involving beta-hydrogen transfer from the alkyl chain, suggestingHybrid density functional calculations on [Cr(NR)2C3H7(C2H4)]+ (R = H, tBu) have revealed a facile reductive elimination reaction involving beta-hydrogen transfer from the alkyl chain, suggesting that the active species in ethylene polymerisation with bis(imido)chromium(VI) precursors contains a reduced chromium atom.

• An investigation of the quantum chemical description of the ethylenic double bond in reactions: II. Insertion of ethylene into a titanium-carbon bond.

  Authors: Vidar R. Jensen, Knut J. Børve

  Journal of Computational Chemistry. 01/1998; 19:947-960.

• Use of multivariate methods in the analysis of calculated reaction pathways.

  Authors: Bjørn K. Alsberg, Vidar R. Jensen, Knut J. Børve

  Journal of Computational Chemistry. 01/1996; 17:1197-1216.

• Catalytic dehydrogenation of ethane over mononuclear Cr(III) surface sites on silica. part I. C - H activation by σ-bond metathesis

  Authors: Sindre Lillehaug, Knut J. Børve, Marek Sierka, Joachim Sauer

  Mononuclear Cr(III)-silica models have been studied by quantum chemical methods with respect to catalytic activity toward dehydrogenation of ethane. Both cluster and slab models have been developedMononuclear Cr(III)-silica models have been studied by quantum chemical methods with respect to catalytic activity toward dehydrogenation of ethane. Both cluster and slab models have been developed and used to explore the conceptual model of mononuclear Cr(III) with three covalent ligands that coordinate through oxygen. The study focuses on a reaction mechanism consisting of three main reaction steps: (1) C - H activation of ethane according to -bond metathesis and accompanied by the formation of O - H and Cr - C bonds, (2) -H transfer to chromium with subsequent loss of ethene and (3) regeneration of the chromium site under evolution of H2. An alternative mechanism is also explored, in which C - H activation takes place at a reactive hydridochromium complex. Stationary points pertaining to these reactions have been optimized, and free energy calculations are used to identify the rate-determining steps. The influence of the local structure of the chromium surface sites is explored by means of a number of idealized surface models and electronic energy profiles for the reactions.

• Second-order Møller–Plesset perturbation theory for computing molecular-field splitting: application to the S2p3/2 level in C2H2n+1SF5, n=0, 1, and 2

  Authors: Tor Karlsen, Knut J. Børve, Leif J. Sæthre

  Chemical Physics.

  High-resolution molecular X-ray photoelectron spectra of second-row atoms may reveal broadening or even splitting of the 2p3/2 peak as compared to the 2p1/2 component of the spectrum. This splittingHigh-resolution molecular X-ray photoelectron spectra of second-row atoms may reveal broadening or even splitting of the 2p3/2 peak as compared to the 2p1/2 component of the spectrum. This splitting reflects the lifted degeneracy of atomic 2p orbitals at sites of less than cubic symmetry and is referred to as molecular-field splitting (MFS). The prospect of using second-order Møller–Plesset theory (MP2) for ab initio calculation of the MFS for sulfur 2p3/2 levels is examined. This method is subsequently applied to compute the MFS in ethynyl, ethenyl, and ethyl sulfur pentafluoride, resulting in values of 80, 116 and 121 meV, respectively. The initial-state contribution to the splitting is analyzed in terms of asymmetry in the electron density at sulfur, on the one hand, and in terms of the sulfur-ligand overlap density and electron density at the groups bonded to sulfur, on the other. At the Koopmans' theorem level of theory, the main source of splitting in the title compounds is found to be s–d hybridization of sulfur. At post-SCF levels of theory, core-valence electron correlation contributes substantially to the MFS, in proportion to the occupational asymmetry of the S3p shell. The realization that mixing of sulfur atomic orbitals of the same parity may add important contributions to the electric-field gradient at the core, resolves the observed diversity in the relative importance of core-valence electron correlation between different classes of sulfur compounds.

• Color and substitution pattern in anthocyanidins. A combined quantum chemical–chemometrical study

  Authors: Kjell Torskangerpoll, Knut J Børve, Øyvind M Andersen, Leif J Sæthre

  Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy.

  The relationship between color and substitution patterns in anthocyanidins has been investigated with the aim of developing quantitative structure–color models. Experimental data for the lowest UVThe relationship between color and substitution patterns in anthocyanidins has been investigated with the aim of developing quantitative structure–color models. Experimental data for the lowest UV transition in 20 substituted anthocyanidins are reviewed. The excitation energies are modeled by semi-empirical ZINDO/S calculations, both at the self-consistent field level of theory and by expanding the excited state in a basis of singly excited configurations (CIS). Even though CIS is required to obtain the right order of magnitude, a better correlation between observed and theoretical excitation energies is achieved through orbital energies according to ΔE=επ*−επ−3.37 eV. At this point, the agreement between theory and experiment is somewhat less than satisfactory. Next, the potential of employing theoretical and positional parameters in a multivariate regression model for the corresponding wavelength (λmax) is explored in terms of the partial least squares (PLS) algorithm. The resulting models substantially improve upon the quantum chemical estimates, and seem to provide high predictive power while keeping the computational cost low. The PLS models are used to address the discrepancy between different experimental λmax values for apigeninidin and luteolinidin reported in the literature.