161 results on '"Leif J. Sæthre"'
Search Results
2. Calibration of oxygen 1s ionization energies. Accurate energies for CO2, H2O, CO, and O2
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T. X. Carroll, P. Wang, Leif J. Sæthre, Knut J. Børve, and T. D. Thomas
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Range (particle radiation) ,Radiation ,Materials science ,Chemical shift ,chemistry.chemical_element ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,chemistry ,Calibration ,Molecule ,Physical and Theoretical Chemistry ,Atomic physics ,Ionization energy ,Adiabatic process ,Carbon ,Absolute scale ,Spectroscopy - Abstract
Access to accurate reference data is a prerequisite in order to translate chemical shifts to an absolute scale for inner-shell ionization energies. Calibration standards for oxygen 1s (O 1s) ionization energies are less well established than, for instance, for carbon 1s. To improve upon this situation, adiabatic and vertical O 1s ionization energies for gaseous carbon dioxide (CO2) are critically reviewed and used to establish the most accurate values currently available: 541.085(17) and 541.253(17) eV, respectively. Combining these with new precise measurements of shifts in O 1s ionization energies for H2O, CO, and O2 allows us to establish equally accurate absolute ionization energies for these molecules as for CO2. The resulting adiabatic and vertical energies are 539.728(17) and 539.827(17) eV for H2O, 542.439(17) and 542.495(17) eV for CO, 543.285(17) and 543.294(17) eV for O2 (4Σ final state), and 544.338(17) and 544.423(17) eV for O2 (2Σ final state). It is proposed that O 1s in CO2 be adopted as a standard of higher precedence, and that H2O, CO, and O2 be used also. The O 1s ionization energies in these molecules occur in the range 540–543 eV. These proposed standards should provide optimal internal calibration for a wide range of oxygen-containing compounds. publishedVersion
- Published
- 2021
3. Energy-dependent relative cross sections in carbon 1s photoionization:separation of direct shake and inelastic scattering effects in single molecules
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Fernando D. Vila, Tatiana Marchenko, Minna Patanen, Johan Söderström, Marc Simon, Oksana Travnikova, Leif J. Sæthre, Loic Journel, John J. Rehr, Denis Céolin, Svante Svensson, Piero Decleva, T. X. Carroll, Renaud Guillemin, Joshua J. Kas, Gildas Goldsztejn, Andreas Lindblad, Knut J. Børve, Nils Mårtensson, Laboratoire de Chimie Physique - Matière et Rayonnement (LCPMR), Institut de Chimie du CNRS (INC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), University of Oulu, Uppsala Universitet [Uppsala], Biorobotics Lab (University of Washington), University of Washington [Seattle], Synchrotron SOLEIL (SSOLEIL), Centre National de la Recherche Scientifique (CNRS), Keuka college, University of Bergen (UiB), Dipartimento di Scienze Chimiche e Farmaceutiche, and Università degli studi di Trieste
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Range (particle radiation) ,010304 chemical physics ,Chemistry ,Shake ,Photoionization ,Photon energy ,Inelastic scattering ,010402 general chemistry ,01 natural sciences ,Molecular physics ,0104 chemical sciences ,Condensed Matter::Soft Condensed Matter ,[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry ,Intramolecular force ,0103 physical sciences ,Theoretical chemistry ,Molecule ,Physical and Theoretical Chemistry - Abstract
International audience; We demonstrate that the possibility of monitoring relative photoionization cross sections over a large photon energy range allows us to study and disentangle shake processes and intramolecular inelastic scattering effects. In this gas-phase study, relative intensities of the carbon 1s photoelectron lines from chemically inequivalent carbon atoms in the same molecule have been measured as a function of the incident photon energy in the range of 300–6000 eV. We present relative cross sections for the chemically shifted carbon 1s lines in the photoelectron spectra of ethyl trifluoroacetate (the “ESCA” molecule). The results are compared with those of methyl trifluoroacetate and S-ethyl trifluorothioacetate as well as a series of chloro-substituted ethanes and 2-butyne. In the soft X-ray energy range, the cross sections show an extended X-ray absorption fine structure type of wiggles, as was previously observed for a series of chloroethanes. The oscillations are damped in the hard X-ray energy range, but deviations of cross-section ratios from stoichiometry persist, even at high energies. The current findings are supported by theoretical calculations based on a multiple scattering model. The use of soft and tender X-rays provides a more complete picture of the dominant processes accompanying photoionization. Such processes reduce the main photoelectron line intensities by 20–60%. Using both energy ranges enabled us to discern the process of intramolecular inelastic scattering of the outgoing electron, whose significance is otherwise difficult to assess for isolated molecules. This effect relates to the notion of the inelastic mean free path commonly used in photoemission studies of clusters and condensed matter.
- Published
- 2019
4. Carbocation stability as predictor for electrophilic addition of HCl to chlorinated ethenes and propenes in the gas phase
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Leif J. Sæthre, Knut J. Børve, Maria G. Zahl, and T. Darrah Thomas
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X-ray photoelectron spectroscopy ,Chemistry ,Electrophilic addition ,Organic Chemistry ,Proton affinity ,Physical and Theoretical Chemistry ,Carbocation ,Photochemistry ,Quantum chemistry ,Gas phase - Published
- 2018
5. Electronic Properties of Chlorine, Methyl, and Chloromethyl as Substituents to the Ethylene Group—Viewed from the Core of Carbon
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T. Darrah Thomas, Leif J. Sæthre, Maria G. Zahl, Knut J. Børve, and Randi Fossheim
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Steric effects ,Chemical shift ,Substituent ,Electronegativity ,chemistry.chemical_compound ,chemistry ,Computational chemistry ,Ab initio quantum chemistry methods ,Moiety ,Matematikk og Naturvitenskap: 400 [VDP] ,Physical and Theoretical Chemistry ,Ionization energy ,Conformational isomerism ,Ethylene Group - Abstract
“Substituent effects” is an important and useful concept in organic chemistry. Although there are many approaches to parametrizing the electronic and steric effects of substituents, the physical basis for the parameters is often unclear. The purpose of the present work is to explore the properties of chemical shifts in carbon 1s energies as a well-defined basis for characterizing substituents to an ethylene C═C moiety. To this end, high-resolution carbon 1s photoelectron spectra of six chloro-substituted ethenes and seven chloro-substituted propenes have been measured in the gas phase. Site-specific adiabatic ionization energies have been determined from the spectra using theoretical ab initio calculations to predict the vibrational structures. For two molecules, 3-chloropropene and 2,3-dichloropropene, the spectral analyses give quantitative results for the conformer populations. The observed shifts have been analyzed in terms of initial-state (potential) and relaxation effects, and charge relaxation has also been analyzed by means of natural resonance theory. On the basis of core-level spectroscopy and models, chlorine, methyl, and chloromethyl have been characterized in terms of their effect on the carbon to which they are attached (α site) as well as the neighboring sp2 carbon (β site). The derived spectroscopic substituent parameters are characterized by both inductive (electronegativity) effects and the ability of each substituent to engage in electron delocalization via the π system. Moreover, the adopted approach is extended to include substituent–substituent interaction parameters. publishedVersion
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- 2015
6. Conformations and CH/π Interactions in Aliphatic Alkynes and Alkenes
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Knut J. Børve, T. Darrah Thomas, Alf Holme, and Leif J. Sæthre
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chemistry.chemical_classification ,Photoemission spectroscopy ,Hydrogen bond ,Alkene ,Chemical shift ,High resolution ,chemistry.chemical_element ,Photochemistry ,Spectral line ,Crystallography ,chemistry ,Physical and Theoretical Chemistry ,Conformational isomerism ,Carbon - Abstract
The carbon 1s photoelectron spectra of a series of aliphatic alkynes and alkenes that have the possibility of possessing two or more conformers have been recorded with high resolution. The two conformers of 2-hexyne and 4-methyl-1-pentyne, anti and gauche, have been identified and quantified from an analysis of their carbon 1s photoelectron spectra, yielding 30 ± 5% and 70 ± 6% anti conformers, respectively. In the case of 1-hexyne, the photoelectron spectrum is shown to provide partial information on the distribution of conformers. Central to these analyses is a pronounced ability of the C1s photoemission process to distinguish between conformers that display weak γ-CH/π hydrogen bonding and those that do not. For the corresponding alkene analogs, similar analyses of their C1s photoelectron spectra do not lead to conclusive information on the conformational equilibria, mainly because of significantly smaller chemical shifts and higher number of conformers compared with the alkynes.
- Published
- 2013
7. Chemical Reactivity of Alkenes and Alkynes As Seen from Activation Energies, Enthalpies of Protonation, and Carbon 1s Ionization Energies
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Leif J. Sæthre, T. Darrah Thomas, Knut J. Børve, and Alf Holme
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chemistry ,Electrophilic addition ,Organic Chemistry ,Molecule ,chemistry.chemical_element ,Protonation ,Ionization energy ,Photochemistry ,Medicinal chemistry ,Carbon - Abstract
Electrophilic addition to multiple carbon-carbon bonds has been investigated for a series of twelve aliphatic and aromatic alkenes and the corresponding alkynes. For all molecules, enthalpies of protonation and activation energies for HCl addition across the multiple bonds have been calculated. Considering the protonation process as a cationic limiting case of electrophilic addition, the sets of protonation enthalpies and gas-phase activation energies allow for direct comparison between double- and triple-bond reactivities in both ionic and dipolar electrophilic reactions. The results from these model reactions show that the alkenes have similar or slightly lower enthalpies of protonation, but have consistently lower activation energies than do the alkynes. These findings are compared with results from high resolution carbon 1s photoelectron spectra measured in the gas phase, where the contribution from carbons of the unsaturated bonds are identified. Linear correlations are found for both protonation and activation energies as functions of carbon 1s energies. However, there are deviations from the lines that reflect differences between the three processes. Finally, substituent effects for alkenes and alkynes are compared using both activation and carbon 1s ionization energies.
- Published
- 2012
8. Carbon 1s photoelectron spectroscopy of the chlorinated methanes: Lifetimes and accurate vibrational lineshape models
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Knut J. Børve, Leif J. Sæthre, and Maria G. Zahl
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Radiation ,Valence (chemistry) ,Chloromethane ,Condensed Matter Physics ,Molecular physics ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Auger ,chemistry.chemical_compound ,X-ray photoelectron spectroscopy ,chemistry ,Computational chemistry ,Ionization ,Molecule ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Spectroscopy ,Excitation ,Dichloromethane - Abstract
Construction of accurate lineshape models for chlorosubstituted hydrocarbons is challenging. In this account the problem has been investigated thoroughly for the chloromethane series, CH4−nCln, n = 1–4, using high-resolution experimental data and extensive theoretical calculations. The C Cl bond contraction following ionization is a key parameter for a quantitative description of the vibrational excitation for all four molecules. We determine this quantity accurately for the title molecules and also propose approximate approaches that may applied to larger molecules. Having developed accurate vibrational lineshape models as well as reliable estimates of the instrumental broadening in each case, the carbon 1s hole lifetime broadening is determined from a fit to the experimental spectrum for each molecule. The resulting values for the lifetime broadening are 88 ± 5 meV for CH3Cl, 80 ± 5 meV for CH2Cl2, 74 ± 5 meV for CHCl3 and 62 ± 5 meV for CCl4. The lifetime widths decrease systematically with the number of chlorine substituents and correlate excellently with the valence occupancy of the core-ionized carbon. This indicates that the one-center model for Auger decay of the core hole is valid for the present series of molecules.
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- 2012
9. The ESCA molecule—Historical remarks and new results
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Nils Mårtensson, Oksana Travnikova, Minna Patanen, Knut J. Børve, Catalin Miron, Svante Svensson, Leif J. Sæthre, and Johan Söderström
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Radiation ,010304 chemical physics ,Photoemission spectroscopy ,Chemistry ,Chemical shift ,Analytical chemistry ,Condensed Matter Physics ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,3. Good health ,Electronic, Optical and Magnetic Materials ,X-ray photoelectron spectroscopy ,0103 physical sciences ,Physical chemistry ,Molecule ,Physical and Theoretical Chemistry ,010306 general physics ,Spectroscopy - Abstract
The C is photoelectron spectrum of ethyl trifluoroacetate (CF3-CO-O-CH2-CH3), also known as the 'ESCA molecule', is the most illustrative showcase of chemical shifts in photoelectron spectroscopy. ...
- Published
- 2012
- Full Text
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10. Accuracy of Calculated Chemical Shifts in Carbon 1s Ionization Energies from Single-Reference ab Initio Methods and Density Functional Theory
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Knut J. Børve, Alf Holme, Leif J. Sæthre, and T. Darrah Thomas
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Physics ,Chemical shift ,Ab initio ,Molecular physics ,Spectral line ,Computer Science Applications ,Experimental uncertainty analysis ,Physics::Atomic and Molecular Clusters ,Density functional theory ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Atomic physics ,Perturbation theory ,Ionization energy ,Adiabatic process - Abstract
A database of 77 adiabatic carbon 1s ionization energies has been prepared, covering linear and cyclic alkanes and alkenes, linear alkynes, and methyl- or fluoro-substituted benzenes. Individual entries are believed to carry uncertainties of less than 30 meV in ionization energies and less than 20 meV for shifts in ionization energies. The database provides an unprecedented opportunity for assessing the accuracy of theoretical schemes for computing inner-shell ionization energies and their corresponding chemical shifts. Chemical shifts in carbon 1s ionization energies have been computed for all molecules in the database using Hartree-Fock, Møller-Plesset (MP) many-body perturbation theory of order 2 and 3 as well as various approximations to full MP4, and the coupled-cluster approximation with single- and double-excitation operators (CCSD) and also including a perturbational estimate of the energy effect of triple-excitation operators (CCSD(T)). Moreover, a wide range of contemporary density functional theory (DFT) methods are also evaluated with respect to computing experimental shifts in C1s ionization energies. Whereas the top ab initio methods reproduce the observed shifts almost to within the experimental uncertainty, even the best-performing DFT approaches meet with twice the root-mean-squared error and thrice the maximum error compared to CCSD(T). However, a number of different density energy functionals still afford sufficient accuracy to become tools in the analysis of complex C1s photoelectron spectra.
- Published
- 2011
11. Size of Free Neutral CO2 Clusters from Carbon 1s Ionization Energies
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J. Harnes, Knut J. Børve, Leif J. Sæthre, M. Winkler, and Andreas Lindblad
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chemistry.chemical_compound ,Monomer ,X-ray photoelectron spectroscopy ,Chemistry ,Cluster (physics) ,Synchrotron radiation ,chemistry.chemical_element ,Physical and Theoretical Chemistry ,Atomic physics ,Ionization energy ,Adiabatic process ,Carbon ,Beam (structure) - Abstract
Free neutral CO2 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, ⟨N⟩, 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 ⟨N⟩ from expansion conditions.
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- 2011
12. Chemical shifts of carbon 1s ionization energies
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T. Darrah Thomas, Leif J. Sæthre, and Knut J. Børve
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Radiation ,Chemistry ,Chemical shift ,Substituent ,chemistry.chemical_element ,Electron ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Molecular conformation ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,X-ray photoelectron spectroscopy ,Molecule ,Physical and Theoretical Chemistry ,Ionization energy ,Atomic physics ,Carbon ,Spectroscopy - Abstract
Third-generation synchrotrons and high-resolution electron spectrometers coupled with modern theoretical techniques for molecular structure calculations have opened opportunities for measuring carbon 1s ionization energies in a large variety of complex molecules. Recent studies have provided new insights into the chemistry of substituent effects and on the effect of molecular conformation on inner-shell ionization energies.
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- 2011
13. Molecular Spectra As a Tool in Assigning Carbon 1s Photoelectron Spectra of Physisorbed Overlayers
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Leif J. Sæthre, J. Harnes, Maria G. Zahl, Velaug Myrseth, Anne Borg, T.H. Andersen, and Knut J. Børve
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Analytical chemistry ,chemistry.chemical_element ,Spectral line ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Propene ,chemistry.chemical_compound ,General Energy ,Adsorption ,chemistry ,Physisorption ,Cyclopentene ,Molecule ,Physical and Theoretical Chemistry ,Ionization energy ,Carbon - Abstract
Carbon 1s photoelectron spectra were measured for 1,1-dichloroethene and 1,3-cyclohexadiene adsorbed on Si(111)-7×7 and for gaseous cyclopentene and 1,1-dichloroethene. We explore closely how the molecular spectra of 1,1-dichloroethene and 1,3-cyclohexadiene change upon physisorption and show how gas-phase X-ray photoelectron spectra can be a useful tool for interpretation of spectra of physisorbed molecules. When assigning spectra of adsorbed states, it is frequently assumed that carbon 1s ionization energies (IE) group according to the hybridization state of the carbon atom and, moreover, that sp3-hybridized carbons have lower ionization energies than do sp2-hybridized carbons. These assumptions are explored by reviewing gas-phase spectra where it is possible to assign spectral peaks to individual carbon atoms without ambiguity. In cyclopentene, the carbon 1s ionization energies do group according to hybridization, albeit with the sp3 carbons at higher IE than the sp2 carbons. In propene, the 1s ionizat...
- Published
- 2010
14. Additivity of Substituent Effects. Core-Ionization Energies and Substituent Effects in Fluoromethylbenzenes
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Knut J. Børve, Leif J. Sæthre, T. X. Carroll, and T. Darrah Thomas
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Fluorobenzenes ,chemistry.chemical_compound ,chemistry ,Computational chemistry ,Substituent ,Molecule ,Protonation ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Ionization energy ,Ring (chemistry) ,Resonance (chemistry) ,Methyl group - Abstract
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 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.
- Published
- 2009
15. Carbon 1s photoelectron spectroscopy of 1-pentyne conformers
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T. D. Thomas, Alf Holme, Knut J. Børve, and Leif J. Sæthre
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Photoemission spectroscopy ,Organic Chemistry ,Resolution (electron density) ,Analytical chemistry ,chemistry.chemical_element ,Analytical Chemistry ,Inorganic Chemistry ,Electron diffraction ,X-ray photoelectron spectroscopy ,chemistry ,Molecule ,Physical chemistry ,Rotational spectroscopy ,Conformational isomerism ,Carbon ,Spectroscopy - Abstract
The carbon 1s photoelectron spectrum of 1-pentyne has been recorded with resolution high enough that contributions from inequivalent carbon atoms can be determined. The spectrum is not well described by theoretical lineshape models that are based on either of the anti or the gauche conformations alone. An improved fit is obtained by combining the two single-conformer models, with the composition determined in the fit. This analysis yields 29 ± 3% anti and 71 ± 3% gauche conformers. This result is in agreement with results based on microwave spectroscopy and gas-phase electron diffraction.
- Published
- 2009
16. Neutral CH3Cl and CH3Br clusters studied by X-ray photoelectron spectroscopy and modeling: Insight to intermolecular interactions and structure
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M. Abu-samha, J. Harnes, Leif J. Sæthre, Knut J. Børve, M. Winkler, and Henrik Bergersen
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Radiation ,Chemistry ,Intermolecular force ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Spectral line ,Electronic, Optical and Magnetic Materials ,Molecular dynamics ,Dipole ,Polarizability ,Ionization ,Cluster (physics) ,Physical and Theoretical Chemistry ,Ionization energy ,Atomic physics ,Spectroscopy - Abstract
Single-component clusters of methyl chloride and methyl bromide have been produced by adiabatic expansion and their C 1s, Cl 2p and Br 3d photoelectron spectra recorded using synchrotron radiation and a high-resolution electron analyzer. The experimentally observed cluster-to-monomer shifts in core-level ionization energies are interpreted in terms of theoretical models based on molecular dynamics (MD) in conjunction with polarizable force fields developed and validated in the course of this work. MD simulations have also been used to explore the global and local structure of the clusters, providing evidence for a predominance of anti-parallel, head-to-tail arrangement of neighboring molecules. Whereas the cluster-to-monomer shifts are strongly dominated by polarization effects, the polarization contribution is very similar for ionization of carbon and the halogen, respectively. The difference in cluster shifts between the two ionization sites within the same molecule, C vs. Cl or C vs. Br, is thus determined by permanent electrostatic moments, i.e. the magnitude and direction of the permanent dipole moment and the local alignment of dipoles.
- Published
- 2008
17. Chemisorption of 1,1-dichloroethene on the Si(1 1 1)-7 × 7 surface
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Anne Borg, Leif J. Sæthre, T.H. Andersen, Knut J. Børve, Maria G. Zahl, and Ingeborg-Helene Svenum
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Silicon ,Chemical shift ,Analytical chemistry ,chemistry.chemical_element ,Surfaces and Interfaces ,Condensed Matter Physics ,Surfaces, Coatings and Films ,chemistry ,X-ray photoelectron spectroscopy ,Chemisorption ,Covalent bond ,Materials Chemistry ,Molecule ,Physical chemistry ,Isomerization ,Carbon - Abstract
Chemisorption of 1,1-dichloroethene (Cl2C CH2) to a Si(1 1 1)-7 × 7 surface was studied by means of X-ray photoelectron spectroscopy using synchrotron radiation, recording chlorine 2p and carbon 1s spectra. For carbon 1s, spectral assignment of the chemisorbed species is based on quantum chemical calculations of chemical shifts in model compounds. The results confirm the identity of covalently bonded 1-chlorovinyl (–CCl CH2) and vinylidene ( C CH2) adspecies. Upon chemisorption at room temperature it was found that about one-third of the molecules break one C–Cl bond while about two-thirds of the adsorbates break two C–Cl bonds. We do not, however, find evidence for isomerization of C CH2 to di-bonded vinylene (–CH CH–).
- Published
- 2007
18. The Substituent Effect of the Methyl Group. Carbon 1s Ionization Energies, Proton Affinities, and Reactivities of the Methylbenzenes
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Knut J. Børve, T. Darrah Thomas, Velaug Myrseth, and Leif J. Sæthre
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Stereochemistry ,Organic Chemistry ,Substituent ,Protonation ,Molar ionization energies of the elements ,Hyperconjugation ,chemistry.chemical_compound ,chemistry ,Ionization ,Physics::Atomic and Molecular Clusters ,Physical chemistry ,Proton affinity ,Ionization energy ,Methyl group - Abstract
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 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.
- Published
- 2007
19. Effects of molecular conformation on inner-shell ionization energies
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Leif J. Sæthre, T. D. Thomas, and Knut J. Børve
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Ions ,Aldehydes ,Hydrocarbons, Fluorinated ,Molecular Conformation ,General Physics and Astronomy ,chemistry.chemical_element ,Molar ionization energies of the elements ,Carbon ,Spectral line ,chemistry.chemical_compound ,Models, Chemical ,chemistry ,Chemical physics ,Nitriles ,Butyronitrile ,Thermodynamics ,Molecule ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Atomic physics ,Ionization energy ,Conformational isomerism ,Methyl group - Abstract
Experimental evidence for an effect of molecular conformation on inner-shell ionization energies has been observed for the first time. Examples are seen in the carbon 1s spectra of butyronitrile, 1-fluoropropane, and propanal, and other similar molecules. At room temperature these exist in two different conformations, with different distances and, hence, different Coulombic interactions between the negatively charged electronegative group and the methyl carbon. The experimental results are in accord with theoretical predictions with respect to both ionization energies and populations of the different conformers.
- Published
- 2007
20. Intensity oscillations in the carbon 1s ionization cross sections of 2-butyne
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T. Darrah Thomas, Fernando D. Vila, John J. Rehr, Joshua J. Kas, T. X. Carroll, Leif J. Sæthre, Piero Decleva, Knut J. Børve, Aurora Ponzi, Maria G. Zahl, Thomas X., Carroll, Maria G., Zahl, Knut J., Bo̸rve, Leif J., Sæthre, Decleva, Pietro, Aurora, Ponzi, Joshua J., Ka, Fernando D., Vila, John J., Rehr, and T., Darrah Thomas
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Ions ,Photons ,Photon ,Chemistry ,Scattering ,Photoelectron Spectroscopy ,General Physics and Astronomy ,Electrons ,Photoionization ,Electron ,Photon energy ,Molecular physics ,Spectral line ,Carbon ,PHOTOELECTRON DIFFRACTION ,Ionization ,Scattering, Radiation ,Density functional theory ,Physical and Theoretical Chemistry ,Atomic physics - Abstract
Carbon 1s photoelectron spectra for 2-butyne (CH3C CCH3) measured in the photon energy range from threshold to 150 eV above threshold show oscillations in the intensity ratio C2,3/C1,4. Similar oscillations have been seen in chloroethanes, where the effect has been attributed to EXAFS-type scattering from the substituent chlorine atoms. In 2-butyne, however, there is no high-Z atom to provide a scattering center and, hence, oscillations of the magnitude observed are surprising. The results have been analyzed in terms of two different theoretical models: a density-functional model with B-spline atom-centered functions to represent the continuum electrons and a multiple-scattering model using muffin-tin potentials to represent the scattering centers. Both methods give a reasonable description of the energy dependence of the intensity ratios.
- Published
- 2013
21. Crystalline products isolated from solutions with commercially available 2,3-bis(2-pyridyl)pyrazine (dpp) as reactant: Detection of a dimerized form of dpp
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Leif J. Sæthre, Hilde Grove, Jorunn Sletten, and Nils Åge Frøystein
- Subjects
Denticity ,Pyrazine ,Stereochemistry ,Hydrogen bond ,Ligand ,Dimer ,Organic Chemistry ,Protonation ,Bridging ligand ,Medicinal chemistry ,Oxalate ,Analytical Chemistry ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Spectroscopy - Abstract
From reaction mixtures of commercially available 2,3-bis(2-pyridyl)pyrazine (dpp) and perchloric acid four different solid products have been isolated and structurally characterized by X-ray crystallography; (dppH2)(ClO4)2·3H2O (1), (dppH2)(ClO4)2 (2), (ddppH2)(ClO4)2 (3) and (dppH)(ClO4) (4) (dppH is monoprotonated dpp, dppH2 is the diprotonated dication of dpp, ddppH2 is the dication 5,5′-bis(2,3-bis(2-pyridyl)pyrazinium), i.e. dimerized dppH). In 1 and 2 the nitrogen atom in both of the pyridyl rings in dpp is protonated. Hydrogen bonding and packing arrangements differ in the two compounds. In 3 a protonated and dimerized form of dpp is found; two 2,3-bis(2-pyridyl)pyrazinium units are connected by a C(sp2) C(sp2) bond in the 5-positions of the pyrazine rings, one pyridyl ring in each dpp moiety being protonated at the nitrogen. Strong intra-cation N H⋯N bonds between pyridyl rings are present. In 4 the monomeric dppH moieties display the same type of intramolecular hydrogen bonds as found in 3. Upon reacting dpp with copper(II) salts and oxalate, a dinuclear copper (II) complex, [Cu2(ddpp)(ox)2(H2O)2] (ddpp = 5,5′-bis(2,3-bis(2-pyridyl)pyrazine)), as well as mononuclear [Cu(dpp)(ox)(H2O)] have been obtained in the same reaction mixtures. In one of the isolated crystalline products a dimer of dpp is found, as described in the case of compound 3, but no protonation has occurred. The crystal structure determination reveals a dinuclear complex with the neutral ddpp (dimerized dpp) as bridging ligand. Oxalate occurs as a bidentate, terminal ligand; water completes the copper coordination sphere. The dinuclear complex cocrystallizes with a mononuclear Cu-dpp-ox complex; in the mixed crystal two mononuclear units replace one dinuclear unit in 25% of the unit cells, thus the average formula is [Cu2(ddpp)(ox)2(H2O)2]0.75[{Cu(dpp)(ox)(H2O)}2]0.25·8H2O (5). The monomeric species also crystallizes in the form of compound 6, [Cu(dpp)(ox)(H2O)]·2H2O. In 6 the dpp ligand and oxalate are both chelating to copper in equatorial positions, and [Cu(dpp)(ox)(H2O)] units are pair-wise connected through weak Cu⋯O (oxalate) interactions (semi-coordination). Geometry optimization through ab initio calculations gave results in good agreement with the experimental molecular geometries of dpp, dppH+ and dppH 2 2 + , respectively. An energy minimum was found for the syn conformation of pyridyl rings in the monoprotonated species, conforming to the existence of the intramolecular N H⋯N hydrogen bond. The compounds containing dimerized dpp were minor products (of the order of 1% yield). To determine whether ddpp had been formed in the reaction mixtures, or had been present as a contaminant in the commercially available dpp, an NMR solution study was performed. Samples of dpp, 1, 3, 4 and ddpp (obtained by treating 3 with base) were investigated by 1H (all five compounds) and 13C NMR (the three former compounds) spectroscopy. The results are consistent with the presence of ddpp as a contaminant in commercially available dpp. The study also allowed us to identify the spectral changes involved in going from neutral dpp to the partial (4) and fully (1) protonated forms.
- Published
- 2006
22. First observation of vibrations in core-level photoelectron spectra of free neutral molecular clusters
- Author
-
Denis Céolin, Gunnar Öhrwall, Leif J. Sæthre, Henrik Bergersen, Olle Björneholm, Knut J. Børve, R. R. T. Marinho, Maxim Tchaplyguine, Svante Svensson, M. Abu-samha, and Andreas Lindblad
- Subjects
Intermolecular force ,General Physics and Astronomy ,Methane ,Spectral line ,Vibration ,chemistry.chemical_compound ,Monomer ,chemistry ,Intramolecular force ,Cluster (physics) ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Atomic physics ,Line (formation) - Abstract
Core-level photoelectron spectra of free neutral methane clusters have been recorded. These spectra exhibit well-resolved surface and bulk features as well as vibrational fine structure. The vibrational structure in the cluster signal is well reproduced by a theoretical model that assumes independent contributions from inter- and intramolecular modes. The intramolecular contribution to the vibrational line-shape is taken to be equal to that of the monomer in the gas phase, while the intermolecular part is simplified to line broadening. An estimate of the cluster size has been made on the basis of the observed surface-to-bulk intensity ratio.
- Published
- 2006
23. Size of neutral argon clusters from core-level photoelectron spectroscopy
- Author
-
Leif J. Sæthre, Olle Björneholm, M. Abu-samha, Henrik Bergersen, Svante Svensson, Knut J. Børve, and J. Harnes
- Subjects
Photons ,Argon ,Photochemistry ,Photoemission spectroscopy ,Spectrum Analysis ,General Physics and Astronomy ,chemistry.chemical_element ,Estimator ,Electrons ,Photoionization ,Spectral line ,Models, Chemical ,X-ray photoelectron spectroscopy ,chemistry ,Cluster size ,Cluster Analysis ,Thermodynamics ,Core level ,Physical and Theoretical Chemistry ,Atomic physics - Abstract
Theoretical models of lineshapes in Ar2p photoionization spectra have been calculated for free, neutral argon clusters of different sizes. The lineshape models are fitted to experimental spectra and used to estimate the mean cluster size realized in the experiment. The results indicate that size estimators working from stagnation conditions [R. Karnbach, M. Joppien, J. Stapelfeldt, J. Wörmer and T.Möller, Rev. Sci. Instrum., 1993, 64, 2838] may underestimate the mean cluster size.
- Published
- 2006
24. Gas-Phase Structure, Conformation, and Sulfur 2p Photoelectron Spectroscopy of Pentafluorosulfur Fluorosulfonate, SF5OSO2F
- Author
-
Leif J. Sæthre, Rolf W. Winter, Gary L. Gard, T. Darrah Thomas, Christiane Leibold, and Heinz Oberhammer
- Subjects
Fluorosulfonate ,Chemistry ,chemistry.chemical_element ,Inorganic Chemistry ,Electronegativity ,Crystallography ,chemistry.chemical_compound ,X-ray photoelectron spectroscopy ,Electron diffraction ,Ionization ,Fluorine ,Physical and Theoretical Chemistry ,Ionization energy ,Conformational isomerism - Abstract
The structure of SF(5)OSO(2)F has been investigated using gas-phase electron diffraction and quantum-chemical calculations. It is found to exist primarily in the gauche form (SF(5) group gauche relative to the S-F bond of the SO(2)F group with phi(S-O-S-F = 71(7) degrees ). A small contribution of the trans conformer cannot be excluded. Photoelectron spectroscopy gives ionization energies for the sulfur 2p electrons that reflect the relative electronegativities of fluorine and oxygen. The widths of the peaks in the photoelectron spectra indicate that there is considerable vibrational excitation associated with the core ionization of the sulfur atoms.
- Published
- 2004
25. Carbon 1s Photoelectron Spectroscopy of Halomethanes. Effects of Electronegativity, Hardness, Charge Distribution, and Relaxation
- Author
-
Leif J. Sæthre, Edwin Kukk, Knut J. Børve, John D. Bozek, Marko Huttula, and T. Darrah Thomas
- Subjects
Chemistry ,Relaxation (NMR) ,chemistry.chemical_element ,Charge density ,Electronegativity ,Linear relationship ,X-ray photoelectron spectroscopy ,Physics::Plasma Physics ,Halogen ,Physics::Atomic and Molecular Clusters ,Physics::Atomic Physics ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Atomic physics ,Ionization energy ,Carbon - Abstract
Carbon 1s ionization energies have been measured for 12 halomethanes. These together with earlier measurements provide 27 compounds for investigating the relationship between core-ionization energies and the electronegativity and hardness of the halogens. The ionization energies correlate nearly linearly with the sum of the electronegativities of the halogens attached to the central carbon. Both electronegativity and hardness play important roles in determining the ionization energy, and it is found that the linear relationship between ionization energy and electronegativity arises from an interplay of the electronegativity and hardness of the halogens and the length and ionicity of the carbon−halogen bond.
- Published
- 2004
26. Carbon 1s photoelectron spectroscopy of six-membered cyclic hydrocarbons
- Author
-
Leif J. Sæthre, Edwin Kukk, T. D. Thomas, John D. Bozek, Knut J. Børve, and V. M. Oltedal
- Subjects
Stereochemistry ,Chemistry ,Photoemission spectroscopy ,General Physics and Astronomy ,chemistry.chemical_element ,Vibronic coupling ,X-ray photoelectron spectroscopy ,Ionization ,Physics::Atomic and Molecular Clusters ,Physical chemistry ,Molecule ,Vibronic spectroscopy ,Physics::Atomic Physics ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Ionization energy ,Carbon - Abstract
The carbon 1s photoelectron spectra of cyclohexane, cyclohexene, 1,3-cyclohexadiene, and 1,4-cyclohexadiene have been measured. These have been analyzed in terms of a theoretical model of the vibronic structure that includes the effects of the changes in equilibrium geometry that accompany core ionization as well as those of vibronic coupling in the core-ionized molecule. This theoretical approach gives an excellent description of the vibronic structure and makes it possible to identify the contributions of the inequivalent carbon atoms to the spectra. The carbon 1s ionization energies are reported and used in the analysis of photoelectron spectra of adsorbed molecules.
- Published
- 2004
27. Xenon N4,5OO Auger spectrum—a useful calibration source
- Author
-
John D. Bozek, Karoline Wiesner, V. Myrseth, T. D. Thomas, T. X. Carroll, Leif J. Sæthre, and Edwin Kukk
- Subjects
Physics ,Auger electron spectroscopy ,3D optical data storage ,Radiation ,Spectrometer ,chemistry.chemical_element ,Electron ,Condensed Matter Physics ,Kinetic energy ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Auger ,Xenon ,chemistry ,Calibration ,Physical and Theoretical Chemistry ,Atomic physics ,Nuclear Experiment ,Spectroscopy - Abstract
In the xenon N 4,5 OO Auger spectrum there are 19 prominent lines ranging in kinetic energy from 8 to 36 eV that provide a convenient set of standards for calibrating electron spectrometers. Combining optical data with recent measurements of this spectrum gives energies for these lines that are absolutely accurate to 11 meV. For most lines the relative accuracy is better than 1 meV; for a few it is about 3 meV. The spin–orbit splitting of the xenon 4d lines is determined to be 1979.0±0.5 meV.
- Published
- 2002
28. Carbon 1s photoelectron spectroscopy of CF4 and CO: Search for chemical effects on the carbon 1s hole-state lifetime
- Author
-
T. Darrah Thomas, Knut J. Børve, Jeffrey A. Hahne, Leif J. Sæthre, Edwin Kukk, John D. Bozek, and T. X. Carroll
- Subjects
chemistry.chemical_classification ,Anharmonicity ,Ab initio ,General Physics and Astronomy ,Bond length ,chemistry.chemical_compound ,chemistry ,X-ray photoelectron spectroscopy ,Ab initio quantum chemistry methods ,Ionization ,Physics::Atomic and Molecular Clusters ,Compounds of carbon ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Atomic physics ,Carbon monoxide - Abstract
Carbon 1s photoelectron spectra for CF4 and CO have been measured at several photon energies near the carbon 1s threshold. The spectra have been analyzed in terms of the vibrational structure and the natural linewidth. For CO the vibrational structure shows evidence for anharmonicity in both the energy spacing and the intensity. Analysis of the results using an anharmonic model gives an equilibrium bond length for core-ionized CO that is 4.85 pm shorter than that of neutral CO. For CF4, the vibrational structure is very weak, and the analysis shows that the change in equilibrium CF bond length upon ionization is no more than 0.54 pm. Ab initio theoretical calculations give results in accord with these bond-length changes. The unusually small bond-length contraction in CF4 can be understood in terms of nonbonded fluorine–fluorine repulsion. The natural linewidth for core-ionized CO, 95±5 meV, is essentially the same as that of CH4. This result is in contrast with expectations based on the one-center model ...
- Published
- 2002
29. Vibrationally resolved photoelectron spectra of the carbon 1s and nitrogen 1s shells in hydrogen cyanide
- Author
-
Knut J. Børve, Karoline Wiesner, Svante Svensson, L. Karlsson, A. Giertz, M. Bäßler, and Leif J. Sæthre
- Subjects
Chemistry ,Ab initio quantum chemistry methods ,Ionization ,Excited state ,Physics::Atomic and Molecular Clusters ,General Physics and Astronomy ,chemistry.chemical_element ,Synchrotron radiation ,Physical and Theoretical Chemistry ,Atomic physics ,Carbon ,Nitrogen ,Spectral line - Abstract
Vibrational structures of the C1s and N1s photoelectron spectra of gas-phase HCN have been investigated using monochromated third-generation synchrotron radiation. Both spectra exhibit resolved fine structure associated with several vibrationally excited states. In the C1s spectrum a single vibrational progression is observed, while the N1s spectrum is more complex. High-level ab initio calculations were performed to simulate the spectra and the agreement with the experimental results is good. Based on the calculations, the C1s ionisation is found to induce vibrations solely in the CN stretching mode with an energy of 280 meV, while the N1s ionisation generates vibrations also in the CH stretching mode with an energy of about 387 meV, as well as combinations of these two modes.
- Published
- 2002
30. Adiabatic and vertical carbon 1s ionization energies in representative small molecules
- Author
-
John D. Bozek, V. Myrseth, T. D. Thomas, Leif J. Sæthre, and Edwin Kukk
- Subjects
Radiation ,Inorganic chemistry ,Analytical chemistry ,chemistry.chemical_element ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Methane ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,chemistry ,Carbon dioxide ,Fluoromethane ,Tetrafluoromethane ,Physical and Theoretical Chemistry ,Ionization energy ,Adiabatic process ,Carbon ,Spectroscopy ,Carbon monoxide - Abstract
Adiabatic and vertical carbon 1s ionization energies are reported for methane (CH 4 ), ethane (CH 3 CH 3 ), ethene (CH 2 CH 2 ), ethyne (HCCH), carbon monoxide (CO), carbon dioxide (CO 2 ), fluoromethane (CH 3 F), trifluoromethane (CHF 3 ), and tetrafluoromethane (CF 4 ) with an absolute accuracy of about 0.03 eV. The results are in good agreement with earlier values but are measured with higher resolution and accuracy than has previously been available.
- Published
- 2002
31. Vibrational structure and vibronic coupling in the carbon 1s photoelectron spectra of benzene and deuterobenzene
- Author
-
M. Bässler, Karoline Wiesner, Svante Svensson, Knut J. Børve, Leif J. Sæthre, and V. Myrseth
- Subjects
Photon ,media_common.quotation_subject ,General Physics and Astronomy ,Synchrotron radiation ,Asymmetry ,Spectral line ,chemistry.chemical_compound ,Vibronic coupling ,chemistry ,Physics::Atomic and Molecular Clusters ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Atomic physics ,Ionization energy ,Benzene ,Excitation ,media_common - Abstract
Vibrationally resolved C1s photoelectron spectra of benzene and d6-benzene have been recorded using monochromated synchrotron radiation at photon energies of 330 eV. The spectrum of normal benzene displays considerable vibrational structure. Particularly noteworthy is the strong excitation of a combined CCH-bending and CC-stretching mode which splits the main peak into two well-defined maxima. In d6-benzene, the vibrational energy levels are less well separated and the vibrational structure is reduced to strong asymmetry of the main peak and a broad tail extending toward higher ionization energy. The recorded spectra are analyzed using first-principle and curve-fitting procedures. A theoretical model that allows for incomplete localization of the core hole, results in very good fits to the experimental spectra of both benzene and d6-benzene.
- Published
- 2002
32. Changing role of carrier gas in formation of ethanol clusters by adiabatic expansion
- Author
-
Einar Uggerud, Knut J. Børve, Mauritz Johan Ryding, M. Abu-samha, and Leif J. Sæthre
- Subjects
Argon ,Valence (chemistry) ,010304 chemical physics ,Chemical shift ,General Physics and Astronomy ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,Synchrotron ,0104 chemical sciences ,law.invention ,X-ray photoelectron spectroscopy ,chemistry ,law ,Chemical physics ,0103 physical sciences ,Cluster (physics) ,Physical and Theoretical Chemistry ,Ionization energy ,Atomic physics ,Adiabatic process - Abstract
Adiabatic expansion of molecular vapors is a celebrated method for producing pure and mixed clusters of relevance in both applied and fundamental studies. The present understanding of the relationship between experimental conditions and the structure of the clusters formed is incomplete. We explore the role of the backing/carrier gas during adiabatic expansion of ethanol vapors with regard to cluster production and composition. Single-component clusters of ethanol were produced over a wide size-range by varying the rare gas (He, Ar) backing pressure, with Ar being more efficient than He in promoting the formation of pure ethanol clusters. However, at stagnation pressures Ps>1.34(4) bar and temperature 49(2) °C, synchrotron-based valence and inner-shell photoelectron spectroscopy reveals condensation of Ar carrier gas on the clusters. Theoretical calculations of cluster geometries as well as chemical shifts in carbon 1s ionization energies confirm that the experimental observations are consistent with an ethanol core covered by an outer shell of argon. Experiments on the 1-propanol/Ar system display a similar pattern as described for ethanol/Ar, indicating a broader range of validity of the results.
- Published
- 2017
33. Line shape and lifetime in argon 2p electron spectroscopy
- Author
-
Leif J. Sæthre, Edwin Kukk, V. Myrseth, John D. Bozek, T. D. Thomas, and T. X. Carroll
- Subjects
Radiation ,Argon ,Photoemission spectroscopy ,chemistry.chemical_element ,Electron ,Condensed Matter Physics ,Electron spectroscopy ,Atomic and Molecular Physics, and Optics ,Spectral line ,Electronic, Optical and Magnetic Materials ,Auger ,chemistry ,Atom ,Physical and Theoretical Chemistry ,Atomic physics ,Spectroscopy ,Line (formation) - Abstract
The argon 2p photoelectron spectrum and the argon L3M23M23 1S0 Auger spectrum have been measured at several photon energies between 6 and 80 eV above the 2p3/2 threshold with an instrumental line width significantly smaller then the natural line width. The spectra are described well by the theory of van der Straten et al. [Z. Phys. D 8 (1988) 35] provided that allowance is made for the instrumental resolution and measurements are made at a sufficiently low pressure. The lifetime (Lorentzian) line width determined from these measurements for the core-ionized atom is 112±3 meV, in good agreement with the line width for the 2p3/2→4s core-excited state, 114±2 meV, indicating that the 4s electron has little influence on the Auger decay rate. Remeasurement of the line width for the carbon 1s hole in carbon dioxide gives values in good agreement with the previous measurement of 99 meV.
- Published
- 2001
34. Vibrational Structure and Vibronic Coupling in the Carbon 1s Photoelectron Spectra of Ethane and Deuteroethane
- Author
-
Nora Berrah, John D. Bozek, Leif J. Sæthre, Edwin Kukk, T. X. Carroll, T. Darrah Thomas, Knut J. Børve, and Tor Karlsen
- Subjects
Vibronic coupling ,law ,Chemistry ,chemistry.chemical_element ,Particle accelerator ,Physical and Theoretical Chemistry ,Atomic physics ,Carbon ,Molecular physics ,Spectral line ,law.invention - Published
- 2001
35. 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
- Author
-
Leif J. Sæthre, Knut J. Børve, and Tor Karlsen
- Subjects
Electron density ,Electronic correlation ,media_common.quotation_subject ,Møller–Plesset perturbation theory ,Ab initio ,General Physics and Astronomy ,chemistry.chemical_element ,Sulfur ,Asymmetry ,Spectral line ,chemistry ,Atomic orbital ,Physics::Atomic and Molecular Clusters ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Atomic physics ,Astrophysics::Galaxy Astrophysics ,media_common - Abstract
High-resolution molecular X-ray photoelectron spectra of second-row atoms may reveal broadening or even splitting of the 2p 3/2 peak as compared to the 2p 1/2 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 Moller–Plesset theory (MP2) for ab initio calculation of the MFS for sulfur 2p 3/2 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.
- Published
- 2001
36. Hydrates of Gadolinium Diethylenetriaminepentaacetic Acid Bis(methylamide) as Studied by X-ray Diffraction
- Author
-
Leiv K. Sydnes, Thoralf Engebretsen, Karl W. Törnroos, Audun Aukrust, and and Leif J. Sæthre
- Subjects
Diffraction ,Gadolinium ,Gadodiamide ,Organic Chemistry ,chemistry.chemical_element ,Methylamide ,Crystal structure ,Diethylenetriaminepentaacetic acid ,Crystallography ,chemistry ,X-ray crystallography ,medicine ,Physical and Theoretical Chemistry ,medicine.drug - Abstract
The crystal structures of two hydrates of the title compound (gadodiamide I and III) have been determined by single-crystal X-ray diffraction. Gadodiamide I crystallises in the non-centrosymmetric ...
- Published
- 2001
37. Molecular-field splitting and vibrational structure in the phosphorus 2p photoelectron spectrum of PF3
- Author
-
Knut J. Bo, T. Darrah Thomas, John D. Bozek, Leif J. Sæthre, rve, and Jan E. True
- Subjects
Field (physics) ,Electronic correlation ,Chemistry ,Photoemission spectroscopy ,General Physics and Astronomy ,Molecular physics ,Bond length ,symbols.namesake ,Atomic orbital ,Ab initio quantum chemistry methods ,Franck–Condon principle ,Ionization ,symbols ,Physical and Theoretical Chemistry ,Atomic physics - Abstract
The experimental phosphorus 2p spectrum of PF3 shows vibrational structure corresponding to the symmetric phosphorus-fluorine stretching mode, with a fundamental frequency of 121.7 meV. In addition, the spectrum shows that the 2p3/2 peak is a doublet split by 146 meV. This molecular-field splitting arises because the anisotropic molecular environment lifts the threefold degeneracy of the 2p orbitals. The observed vibrational structure is compared with that predicted by theory, either treating the core hole explicitly or using the equivalent-cores approximation to simulate the effects of the core hole. Ab initio calculations of the molecular-field splitting that include core-valence electron correlation predict a value in good agreement with the experimental value.
- Published
- 1999
38. Molecular-field splitting in S2p photoelectron spectra of dimethyl sulfide and sulfur dichloride
- Author
-
Svante Svensson, Leif J. Sæthre, and Knut J. Børve
- Subjects
Electronic correlation ,Field (physics) ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,Sulfur ,Spectral line ,chemistry.chemical_compound ,chemistry ,Ab initio quantum chemistry methods ,Physics::Atomic and Molecular Clusters ,Sulfur dichloride ,Dimethyl sulfide ,Physics::Chemical Physics ,Physical and Theoretical Chemistry - Abstract
High-resolution S2p photoelectron spectra have been measured for sulfur dichloride and dimethyl sulfide. By means of efficient fitting procedures and theoretical analyses, the vibrational fine structure has been disentangled from the molecular-field induced splitting of the S2p3/2 core-ionized level. The resulting molecular-field splitting is determined to be 177 meV in the case of SCl2 and 104 meV for (CH3)2S. Ab initio calculations that include core–valence electron correlation are able to reproduce these values to within 3 meV. Theoretical predictions of the molecular-field splitting are presented for a series of related sulfur compounds, SX2, where X=H, NH2, CN, and F.
- Published
- 1999
39. Carbon1sphotoelectron spectrum of methane: Vibrational excitation and core-hole lifetime
- Author
-
Leif J. Sæthre, John D. Bozek, J. Hahne, E. Kukk, T. D. Thomas, Nora Berrah, and T. X. Carroll
- Subjects
Physics ,Photon ,Photoemission spectroscopy ,Anharmonicity ,Kinetic isotope effect ,Electron ,Atomic physics ,Photon energy ,Atomic and Molecular Physics, and Optics ,Spectral line ,Excitation - Abstract
The carbon $1s$ photoelectron spectrum has been measured for ${\mathrm{CH}}_{4}$ at photon energies of 302, 320, and 330 eV and for ${\mathrm{CD}}_{4}$ at 330 eV with an instrumental resolution about half the natural linewidth. These spectra have been analyzed to obtain vibrational spacings, vibrational intensities, and the lifetime of the carbon $1s$ core-hole state. The vibrational intensities vary with photon energy, in agreement with earlier results. At 330 eV, the observed Franck-Condon factors for both ${\mathrm{CH}}_{4}$ and ${\mathrm{CD}}_{4}$ can be understood only if anharmonic effects (consistent with the predictions of theory) are included. On the other hand, the vibrational spacings in ${\mathrm{CH}}_{4}$ show no evidence for anharmonicity (in contrast with theoretical predictions). In ${\mathrm{CD}}_{4}$ the observed anharmonicity in the vibrational energy spacings is about half of the predicted value, but the experimental and theoretical values differ only by an amount comparable to the experimental uncertainty. The measured values of the lifetime show a dependence on photon energy; this is attributed to failure of the theory of post-collision interaction to predict correctly the observed electron spectrum near threshold. At 330 eV, the measured Lorentzian lifetime, 93--95 meV, agrees with predictions of simple theory, but not with the prediction of more complete theory. It is also observed that there are systematic discrepancies between the observed line shapes and those predicted by the theory of postcollision interaction.
- Published
- 1999
40. Color and substitution pattern in anthocyanidins. A combined quantum chemical–chemometrical study
- Author
-
Leif J. Sæthre, Øyvind M. Andersen, Kjell Torskangerpoll, and Knut J. Børve
- Subjects
Field (physics) ,Chemistry ,Analytical chemistry ,Molecular physics ,Atomic and Molecular Physics, and Optics ,Analytical Chemistry ,Anthocyanidins ,Wavelength ,Excited state ,Partial least squares regression ,ZINDO ,Instrumentation ,Spectroscopy ,Order of magnitude ,Excitation - Abstract
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 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=eπ*−eπ−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.
- Published
- 1999
41. Vibrational structure of the chloromethane series, CH4−nCln, studied by core photoelectron spectroscopy and ab initio calculations
- Author
-
A. Ausmees, S. Sundin, S. Svensson, S. L. Sorensen, and Leif J. Sæthre
- Subjects
Series (mathematics) ,Physics::Instrumentation and Detectors ,Chloromethane ,General Physics and Astronomy ,Electron spectroscopy ,Molecular physics ,Spectral line ,chemistry.chemical_compound ,X-ray photoelectron spectroscopy ,chemistry ,Ab initio quantum chemistry methods ,Physics::Atomic and Molecular Clusters ,Molecule ,Physical chemistry ,Physics::Atomic Physics ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Ionization energy - Abstract
Vibrationally resolved C1s photoelectron spectra of the chloromethane series, CH4-nCln, are reported. The spectra are compared with results from ab initio calculations at the MP2 level using the Z+ ...
- Published
- 1999
42. Photon Energy Dependence of the1σu/1σgIntensity Ratio in Carbon1sPhotoelectron Spectroscopy of Ethyne
- Author
-
J. Hahne, Tor Karlsen, E. Kukk, John D. Bozek, Nora Berrah, T. D. Thomas, T. X. Carroll, and Leif J. Sæthre
- Subjects
Physics ,Shape resonance ,Atomic orbital ,Photoemission spectroscopy ,Ionization ,General Physics and Astronomy ,Sigma ,Photoionization ,Photon energy ,Atomic physics ,Energy (signal processing) - Abstract
High-resolution measurements of the C 1s photoelectron spectrum of ethyne (acetylene) at photon energies between 297 and 348thinspthinspeV have been analyzed to give the energy dependence of the relative cross sections for ionization of the 1{sigma}{sub g} and 1{sigma}{sub u} orbitals. The 1{sigma}{sup {minus}1}{sub u}/1{sigma}{sup {minus}1}{sub g} intensity ratio is greater than 1 at the lowest photon energies but reaches a minimum of about 0.6 between 315 and 320thinspthinspeV. These results can be understood in terms of the effect of shape resonance on the ionization cross section and provide quantitative information on the position and magnitude of such resonances. {copyright} {ital 1999} {ital The American Physical Society}
- Published
- 1999
43. Methylphenanthrenecarbaldehydes by Selective Cerium(IV) Oxidation of Dimethylphenanthrenes
- Author
-
Leiv K. Sydnes, Ivan C. Burkow, Mona Kvivesen, Leif J. Sæthre, Markku Ahlgrén, Jouni Pursiainen, Hong-Gen Wang, Xin-Kan Yao, J. -P. Tuchagues, and Mattias Ögren
- Subjects
Cerium ,chemistry ,General Chemical Engineering ,chemistry.chemical_element ,Nuclear chemistry - Published
- 1999
44. Vibrational structure in the carbon 1s ionization of hydrocarbons: Calculation using electronic structure theory and the equivalent-cores approximation
- Author
-
Leif J. Sæthre, Svante Svensson, Stacey L. Sorensen, and T. Darrah Thomas
- Subjects
Chemistry ,Ab initio ,General Physics and Astronomy ,Electronic structure ,Molecular physics ,Spectral line ,Ab initio quantum chemistry methods ,Ionization ,Molecular vibration ,Physics::Atomic and Molecular Clusters ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Ionization energy ,Atomic physics ,Harmonic oscillator - Abstract
A simple ab initio procedure is used to calculate the vibrational structure observed in the carbon 1s ionization of seven hydrocarbons (methane, deuteromethane, ethane, ethene, deuteroethene, ethyne, and deuteroethyne), with good agreement between experiment and theory. The method involves use of the equivalent-cores approximation, localized holes in molecules with equivalent carbons, and the harmonic oscillator approximation. The approach provides insight into the vibrational modes of the core-ionized molecules. It is potentially useful in extracting carbon 1s ionization energies from spectra from molecules having inequivalent carbons or in finding information on inner-hole lifetimes from inner-shell spectra.
- Published
- 1998
45. High-resolution carbon1sphotoelectron spectrum of ethene: Ab initiocalculation of vibrational structure with dynamic localization of the core hole
- Author
-
J. Hahne, T. D. Thomas, T. X. Carroll, J. True, John D. Bozek, and Leif J. Sæthre
- Subjects
Physics ,X-ray photoelectron spectroscopy ,Photoemission spectroscopy ,Ab initio quantum chemistry methods ,Resolution (electron density) ,Ab initio ,Sigma ,Electronic structure ,Atomic physics ,Atomic and Molecular Physics, and Optics ,Spectral line - Abstract
The vibrational structure in the carbon 1s photoelectron spectrum of ethene has been measured with a total experimental resolution of about 55 meV, significantly better than has been previously reported. The spectrum has been calculated using {ital ab initio} electronic structure theory with a localized core hole and the equivalent-cores approximation. Agreement between the calculated spectrum and measurements (taken 29 eV above the carbon 1s threshold) is excellent. This agreement indicates that there is dynamic localization of the core hole, even though the 1{sigma}{sub g}-1{sigma}{sub u} splitting is not small. The theoretical method provides an approach that is useful for analyzing such spectra and also shows some of the pitfalls of attempting to fit complex vibrational spectra without guidance from theory. {copyright} {ital 1998} {ital The American Physical Society}
- Published
- 1998
46. High-resolution C 1s photoelectron spectra of methane, ethene, propene, and 2-methylpropene
- Author
-
Leif J. Sæthre, Svante Svensson, S. J. Osborne, O. Svaeren, J. Jauhiainen, T. D. Thomas, and Seppo Aksela
- Subjects
Physics ,Photoionization ,Molecular physics ,Atomic and Molecular Physics, and Optics ,Spectral line ,Propene ,chemistry.chemical_compound ,chemistry ,Ab initio quantum chemistry methods ,Ionization ,Physics::Atomic and Molecular Clusters ,Physics::Atomic Physics ,Physics::Chemical Physics ,Ionization energy ,Spectroscopy ,Excitation - Abstract
Vibrational fine structure in the C 1s photoelectron spectra of methane, ethene, propene, and 2-methylpropene has been observed using high-resolution synchrotron radiation. The degree of vibrational excitation is found to increase with the number of hydrogens attached to the core-ionized carbon atom, and this observation can be rationalized using a linear coupling intensity model. The vibrational structure can be accounted for almost quantitatively with the assumption that the primary vibrational excitation is stretching of the CH bond attached to the core-ionized carbon atom, using the results from methane to establish the intensities of the CH stretching vibrations in the other molecules. Ab initio calculations of the geometrical changes accompanying C 1s core ionization support this picture. The high resolution in these experiments makes it possible to determine the core-ionization energies of the inequivalent carbons in propene and 2-methylpropene, as well as the difference between the adiabatic and vertical ionization energies in all four molecules. Ab initio calculations of vertical binding-energy shifts using hole-state calculations show good agreement with those determined experimentally.
- Published
- 1997
47. Markovnikov addition to alkenes. A different view from core-electron spectroscopy and theory
- Author
-
T. D. Thomas, Svante Svensson, and Leif J. Sæthre
- Subjects
Binding energy ,Markovnikov's rule ,Charge density ,Molar ionization energies of the elements ,Propene ,chemistry.chemical_compound ,chemistry ,Core electron ,Computational chemistry ,Ab initio quantum chemistry methods ,Physics::Atomic and Molecular Clusters ,Physical chemistry ,Physics::Chemical Physics ,Ionization energy - Abstract
Carbon 1s ionization energies for ethene, propene and 2-methylpropene have been measured in the gas phase at high resolution using synchrotron radiation and analysed by means of ab initio calculations. For the first time, resolution is good enough to assign ionization energies to the inequivalent carbons in propene and 2-methylpropene. A linear correlation is found between the ionization energies and activation energies for addition of the electrophiles HF, HCl, HBr and HI to these molecules. The correlation shows that both reactivity and regiospecificity are quantitatively related to core-ionization energies. Theoretical analysis of the core-ionization energies shows that the differences between ionization energies for the doubly bonded carbons are due to the charge distribution in the unionized molecule. Theoretical analysis of the transition state for addition of HCl to propene and 2-methylpropene indicates that a significant portion of the difference between Markovnikov and anti-Markovnikov addition is also due to the charge distribution in the initial state and not to different ability of the molecules to delocalize the added charge in the transition state. The increase in reactivity with the number of methyl groups is also strongly influenced by the initial-state charge distribution.
- Published
- 1997
48. Laboratory-frame electron angular distributions: Probing the chemical environment through intramolecular electron scattering
- Author
-
Minna Patanen, Nils Mårtensson, Piero Decleva, Johan Söderström, Oksana Travnikova, C. Miron, Maria G. Zahl, Knut J. Børve, Leif J. Sæthre, Svante Svensson, T. D. Thomas, M., Patanen, O., Travnikova, M. G., Zahl, J., Söderström, Decleva, Pietro, T. D., Thoma, S., Svensson, N., Mårtensson, K. J., Børve, L. J., Sæthre, and C., Miron
- Subjects
Physics ,010304 chemical physics ,photoelectron asymmetry parameter ,chemistry.chemical_element ,Synchrotron radiation ,Photoionization ,Electron ,01 natural sciences ,Molecular physics ,Atomic and Molecular Physics, and Optics ,chemistry ,Ab initio quantum chemistry methods ,Intramolecular force ,Physical Sciences ,CF4 photoionization ,0103 physical sciences ,Atom ,Fysik ,Physics::Chemical Physics ,Atomic physics ,010306 general physics ,Carbon ,Electron scattering - Abstract
Carbon 1s photoelectron asymmetry parameters beta for the chlorinated and the methyl carbon atom of CH3CH2Cl, CH3CHCl2, and CH3CCl3 have been measured using synchrotron radiation in the 340-600 eV energy range. We provide experimental evidence that the intramolecular scattering strongly affects beta values, even far from the ionization threshold. The results are in agreement with B-spline density functional theory calculations, making it possible to single out the behavior of the various continuum partial waves. We conclude that the intramolecular scattering makes electron angular distributions sensitive to the chemical environment, even in isolated gas phase molecules.
- Published
- 2013
49. High resolution photoelectron spectroscopy of sulfur 2p electrons in H2S, SO2, CS2, and OCS
- Author
-
Christian N. Field, Leif J. Sæthre, Knut J. Bo, T. Darrah Thomas, Michele R. F. Siggel, and rve
- Subjects
X-ray photoelectron spectroscopy ,Field (physics) ,Chemistry ,Ab initio quantum chemistry methods ,Hartree–Fock method ,General Physics and Astronomy ,Electron ,Physical and Theoretical Chemistry ,Atomic physics ,Configuration interaction ,Excitation ,Spectral line - Abstract
High‐resolution photoelectron spectra for the 2p electrons in H2S, SO2, CS2, and OCS show the effects of vibrational excitation in the core‐excited species as well as the splitting of the 2p3/2 hole state by the molecular field. Theoretical calculations at the Hartree–Fock level account reasonably well for the vibrational structure. The molecular‐field splitting is calculated with a configuration interaction‐based method using large basis sets. This produces values for the 2p3/2 splitting of 108, 96, 129, and 144 meV for the title molecules, to be compared with experimental values of 110, 105, 140, and 150 meV. Thus all observed features in the spectra are quantitatively accounted for by theoretical modeling.
- Published
- 1996
50. Nonstoichiometric Intensities in Core Photoelectron Spectroscopy
- Author
-
T. D. Thomas, Svante Svensson, Knut J. Børve, Leif J. Sæthre, Johan Söderström, Fernando D. Vila, Joshua J. Kas, Minna Patanen, Catalin Miron, John J. Rehr, Oksana Travnikova, and Nils Mårtensson
- Subjects
Materials science ,010304 chemical physics ,Extended X-ray absorption fine structure ,Photoemission spectroscopy ,Scattering ,Inverse photoemission spectroscopy ,General Physics and Astronomy ,Angle-resolved photoemission spectroscopy ,Inelastic scattering ,7. Clean energy ,01 natural sciences ,Molecular physics ,Condensed Matter::Materials Science ,Nuclear magnetic resonance ,Condensed Matter::Superconductivity ,Ionization ,0103 physical sciences ,010306 general physics ,Spectroscopy - Abstract
X-ray photoemission spectroscopy is used in a great variety of research fields; one observable is the sample's stoichiometry. The stoichiometry can be deduced based on the expectation that the ionization cross sections for innershell orbitals are independent of the molecular composition. Here we used chlorine-substituted ethanes in the gas phase to investigate the apparent carbon stoichiometry. We observe a nonstoichiometric ratio for a wide range of photon energies, the ratio exhibits x-ray-absorption fine structure spectroscopy (EXAFS)-like oscillations and hundreds of eV above the C1s ionization approaches a value far from 1. These effects can be accounted for by considering the scattering of the outgoing photoelectron, which we model by multiple-scattering EXAFS calculations, and by considering the effects of losses due to monopole shakeup and shakeoff and to intramolecular inelastic scattering processes.
- Published
- 2012
- Full Text
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