Change search
Refine search result
1 - 16 of 16
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1. Beye, M.
    et al.
    Anniyev, T.
    Coffee, R.
    Dell'Angela, M.
    Foehlisch, A.
    Gladh, Jörgen
    Stockholm University, Faculty of Science, Department of Physics.
    Katayama, T.
    Kaya, S.
    Krupin, O.
    Mogelhoj, A.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics. SLAC National Accelerator Laboratory, USA.
    Nordlund, D.
    Norskov, J. K.
    Öberg, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Ogasawara, H.
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Schlotter, W. F.
    Sellberg, Jonas
    Stockholm University, Faculty of Science, Department of Physics. SLAC National Accelerator Laboratory, USA.
    Sorgenfrei, F.
    Turner, J. J.
    Wolf, M.
    Wurth, W.
    Öström, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Selective Ultrafast Probing of Transient Hot Chemisorbed and Precursor States of CO on Ru(0001)2013In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 110, no 18, article id 186101Article in journal (Refereed)
    Abstract [en]

    We have studied the femtosecond dynamics following optical laser excitation of CO adsorbed on a Ru surface by monitoring changes in the occupied and unoccupied electronic structure using ultrafast soft x-ray absorption and emission. We recently reported [M. Dell'Angela et al. Science 339, 1302 (2013)] a phonon-mediated transition into a weakly adsorbed precursor state occurring on a time scale of >2 ps prior to desorption. Here we focus on processes within the first picosecond after laser excitation and show that the metal-adsorbate coordination is initially increased due to hot-electron-driven vibrational excitations. This process is faster than, but occurs in parallel with, the transition into the precursor state. With resonant x-ray emission spectroscopy, we probe each of these states selectively and determine the respective transient populations depending on optical laser fluence. Ab initio molecular dynamics simulations of CO adsorbed on Ru(0001) were performed at 1500 and 3000 K providing insight into the desorption process.

  • 2. Beye, Martin
    et al.
    Öberg, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Xin, Hongliang
    Dakovski, Georgi L.
    Dell'Angela, Martina
    Föhlisch, Alexander
    Gladh, Jörgen
    Stockholm University, Faculty of Science, Department of Physics.
    Hantschmann, Markus
    Hieke, Florian
    Kaya, Sarp
    Kuehn, Danilo
    LaRue, Jerry
    Mercurio, Giuseppe
    Minitti, Michael P.
    Mitra, Ankush
    Stockholm University, Faculty of Science, Department of Physics.
    Moeller, Stefan P.
    Ng, May Ling
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics. SLAC National Accelerator Laboratory, United States.
    Nordlund, Dennis
    Norskov, Jens
    Östrom, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Ogasawara, Hirohito
    Persson, Mats
    Schlotter, William F.
    Sellberg, Jonas A.
    Stockholm University, Faculty of Science, Department of Physics. KTH Royal Institute of Technology, Sweden; SLAC National Accelerator Laboratory, United States.
    Wolf, Martin
    Abild-Pedersen, Frank
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Wurth, Wilfried
    Chemical Bond Activation Observed with an X-ray Laser2016In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 7, no 18, p. 3647-3651Article in journal (Refereed)
    Abstract [en]

    The concept of bonding and antibonding orbitals is fundamental in chemistry. The population of those orbitals and the energetic difference between the two reflect the strength of the bonding interaction. Weakening the bond is expected to reduce this energetic splitting, but the transient character of bond-activation has so far prohibited direct experimental access. Here we apply time-resolved soft X-ray spectroscopy at a free electron laser to directly observe the decreased bonding antibonding splitting following bond-activation using an ultrashort optical laser pulse.

  • 3. Dell'Angela, M.
    et al.
    Anniyev, T.
    Beye, M.
    Coffee, R.
    Foehlisch, A.
    Gladh, Jörgen
    Stockholm University, Faculty of Science, Department of Physics.
    Katayama, T.
    Kaya, S.
    Krupin, O.
    LaRue, J.
    Mogelhoj, A.
    Nordlund, D.
    Norskov, J. K.
    Öberg, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Ogasawara, H.
    Öström, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Schlotter, W. F.
    Sellberg, Jonas A.
    Stockholm University, Faculty of Science, Department of Physics. SLAC National Accelerator Laboratory, USA.
    Sorgenfrei, F.
    Turner, J. J.
    Wolf, M.
    Wurth, W.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics. SLAC National Accelerator Laboratory, USA.
    Real-Time Observation of Surface Bond Breaking with an X-ray Laser2013In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 339, no 6125, p. 1302-1305Article in journal (Refereed)
    Abstract [en]

    We used the Linac Coherent Light Source free-electron x-ray laser to probe the electronic structure of CO molecules as their chemisorption state on Ru(0001) changes upon exciting the substrate by using a femtosecond optical laser pulse. We observed electronic structure changes that are consistent with a weakening of the CO interaction with the substrate but without notable desorption. A large fraction of the molecules (30%) was trapped in a transient precursor state that would precede desorption. We calculated the free energy of the molecule as a function of the desorption reaction coordinate using density functional theory, including van der Waals interactions. Two distinct adsorption wells-chemisorbed and precursor state separated by an entropy barrier-explain the anomalously high prefactors often observed in desorption of molecules from metals.

  • 4.
    Gladh, Jörgen
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Öberg, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Li, Jibiao
    Stockholm University, Faculty of Science, Department of Physics.
    Ljungberg, M. P.
    Stockholm University, Faculty of Science, Department of Physics.
    Matsuda, A.
    Stockholm University, Faculty of Science, Department of Physics.
    Ogasawara, H.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics. Stanford Synchrotron Radiation Lightsource, USA.
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Öström, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    X-ray emission spectroscopy and density functional study of CO/Fe(100)2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 136, no 3, article id 034702Article in journal (Refereed)
    Abstract [en]

    We report x-ray emission and absorption spectroscopy studies of the electronic structure of the pre-dissociative alpha(3) phase of CO bound at hollow sites of Fe(100) as well as of the on-top bound species in the high-coverage alpha(1) phase. The analysis is supported by density functional calculations of structures and spectra. The bonding of lying down CO in the hollow site is well described in terms of pi to pi* charge transfer made possible through bonding interaction also at the oxygen in the minority spin-channel. The on-top CO in the mixed, high-coverage alpha(1) phase is found to be tilted due to adsorbate-adsorbate interaction, but still with bonding mainly characteristic of vertical on-top adsorbed CO similar to other transition-metal surfaces.

  • 5.
    Gladh, Jörgen
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Öberg, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Öström, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Detection of adsorbate overlayer structural transitions using sum-frequency generation spectroscopy2015In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 633, p. 77-81Article in journal (Refereed)
    Abstract [en]

    We demonstrate that temperature-programmed vibrational sum-frequency generation (SFG) spectroscopy has a unique sensitivity to certain adsorbate overlayer structural transitions. In the CO stretching vibration of co-adsorbed CO/O(2x1)/Ru(0001) we observe pronounced dips in the spectral intensity as the adsorbate overlayer undergoes structural transitions with temperature. Combining with temperature-programmed desorption (TPD) a more complete picture of temperature-dependent structural transitions is obtained. We extract kinetic parameters from the SFG data and obtain good agreement with TPD when both techniques see the same transition. Infrared-infrared visible SFG is used to determine changes in inter-adsorbate coupling that allow us to experimentally assign the structural transitions. Furthermore, density functional theory calculations of the proposed structures and energetics are performed to verify the experimental assignments.

  • 6. Miller, D. J.
    et al.
    Öberg, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Kaya, S.
    Casalongue, H. Sanchez
    Friebel, D.
    Anniyev, T.
    Ogasawara, H.
    Bluhm, H.
    Pettersson, Lars G.M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Oxidation of Pt(111) under Near-Ambient Conditions2011In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, no 19, p. 195502-Article in journal (Refereed)
    Abstract [en]

    The oxidation of Pt(111) at near-ambient O(2) pressures has been followed in situ using x-ray photoelectron spectroscopy (XPS) and ex situ using x-ray absorption spectroscopy (XAS). Polarization-dependent XAS signatures at the O K edge reveal significant temperature-and pressure-dependent changes of the Pt-O interaction. Oxide growth commences via a PtO-like surface oxide that coexists with chemisorbed oxygen, while an ultrathin alpha-PtO(2) trilayer is identified as the precursor to bulk oxidation. These results have important implications for understanding the chemical state of Pt in catalysis.

  • 7.
    Miller, Daniel J.
    et al.
    Stanford.
    Öberg, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Näslund, Lars-Åke
    Stanford.
    Anniyev, Toyli
    Stanford.
    Ogasawara, Hirohito
    Stanford.
    Pettersson, Lars G.M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Low O-2 dissociation barrier on Pt(111) due to adsorbate-adsorbate interactions2010In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, no 22, p. 224701-Article in journal (Refereed)
    Abstract [en]

    O2 dissociation on Pt(111) has been followed at low and saturation coverage using temperature-programmed x-ray photoelectron spectroscopy and simulated with mean-field kinetic modeling, yielding dissociation (Ea) and desorption (Ed) barriers of 0.32 and 0.36 eV, respectively. DFT calculations show that Ea is strongly influenced by the O–O interatomic potential in the atomic final state: of the supercells considered, that which maximizes attractive third-nearest-neighbor interactions in the atomic final state yields both the lowest computed dissociation barrier (0.24 eV) and the best agreement with experiment. It is proposed that the effect of adsorbate-adsorbate interactions must be considered when modeling catalytic processes involving dissociative steps.

  • 8.
    Nilsson, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    LaRue, J.
    Öberg, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Ogasawara, H.
    Dell'Angela, M.
    Beye, M.
    Öström, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Gladh, Jörgen
    Stockholm University, Faculty of Science, Department of Physics.
    Nørskov, J. K.
    Wurth, W.
    Abild-Pedersen, F.
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Catalysis in real time using X-ray lasers2017In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 675, p. 145-173Article in journal (Refereed)
    Abstract [en]

    We describe how the unique temporal and spectral characteristics of X-ray free-electron lasers (XFEL) can be utilized to follow chemical transformations in heterogeneous catalysis in real time. We highlight the systematic study of CO oxidation on Ru(0001), which we initiate either using a femtosecond pulse from an optical laser or by activating only the oxygen atoms using a THz pulse. We find that CO is promoted into an entropy-controlled precursor state prior to desorbing when the surface is heated in the absence of oxygen, whereas in the presence of oxygen, CO desorbs directly into the gas phase. We monitor the activation of atomic oxygen explicitly by the reduced split between bonding and antibonding orbitals as the oxygen comes out of the strongly bound hollow position. Applying these novel XFEL techniques to the full oxidation reaction resulted in the surprising observation of a significant fraction of the reactants at the transition state through the electronic signature of the new bond formation.

  • 9. Xin, H.
    et al.
    LaRue, J.
    Öberg, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Beye, M.
    Dell'Angela, M.
    Turner, J. J.
    Gladh, Jörgen
    Stockholm University, Faculty of Science, Department of Physics.
    Ng, M. L.
    Sellberg, Jonas A.
    Stockholm University, Faculty of Science, Department of Physics.
    Kaya, S.
    Mercurio, G.
    Hieke, F.
    Nordlund, D.
    Schlotter, W. F.
    Dakovski, G. L.
    Minitti, M. P.
    Foehlisch, A.
    Wolf, M.
    Wurth, W.
    Ogasawara, H.
    Norskov, J. K.
    Östrom, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics. SLAC National Accelerator Laboratory, USA.
    Abild-Pedersen, E.
    Strong Influence of Coadsorbate Interaction on CO Desorption Dynamics on Ru(0001) Probed by Ultrafast X-Ray Spectroscopy and Ab Initio Simulations2015In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 114, no 15, article id 156101Article in journal (Refereed)
    Abstract [en]

    We show that coadsorbed oxygen atoms have a dramatic influence on the CO desorption dynamics from Ru(0001). In contrast to the precursor-mediated desorption mechanism on Ru(0001), the presence of surface oxygen modifies the electronic structure of Ru atoms such that CO desorption occurs predominantly via the direct pathway. This phenomenon is directly observed in an ultrafast pump-probe experiment using a soft x-ray free-electron laser to monitor the dynamic evolution of the valence electronic structure of the surface species. This is supported with the potential of mean force along the CO desorption path obtained from density-functional theory calculations. Charge density distribution and frozen-orbital analysis suggest that the oxygen-induced reduction of the Pauli repulsion, and consequent increase of the dative interaction between the CO 5 sigma and the charged Ru atom, is the electronic origin of the distinct desorption dynamics. Ab initio molecular dynamics simulations of CO desorption from Ru(0001) and oxygen-coadsorbed Ru(0001) provide further insights into the surface bond-breaking process.

  • 10.
    Öberg, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Surface reactions and chemical bonding in heterogeneous catalysis2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis summarizes studies which focus on addressing, using both theoretical and experimental methods, fundamental questions about surface phenomena, such as chemical reactions and bonding, related to processes in heterogeneous catalysis. The main focus is on the theoretical approach and this aspect of the results. The included articles are collected into three categories of which the first contains detailed studies of model systems in heterogeneous catalysis. For example, the trimerization of acetylene adsorbed on Cu(110) is measured using vibrational spectroscopy and modeled within the framework of Density Functional Theory (DFT) and quantitative agreement of the reaction barriers is obtained. In the second category, aspects of fuel cell catalysis are discussed. O2 dissociation is rate-limiting for the reduction of oxygen (ORR) under certain conditions and we find that adsorbate-adsorbate interactions are decisive when modeling this reaction step. Oxidation of Pt(111) (Pt is the electrocatalyst), which may alter the overall activity of the catalyst, is found to start via a PtO-like surface oxide while formation of α-PtO2 trilayers precedes bulk oxidation. When considering alternative catalyst materials for the ORR, their stability needs to be investigated in detail under realistic conditions. The Pt/Cu(111) skin alloy offers a promising candidate but segregation of Cu atoms to the surface is induced by O adsorption. This is confirmed by modeling oxygen x-ray emission (XES) and absorption spectra of the segregated system and near-perfect agreement with experiment is obtained when vibrational interference effects are included in the computed XES. The last category shows results from femtosecond laser measurements of processes involving CO on Ru(0001). Using free-electron x-ray laser experiments a precursor state to desorption is detected and also found in simulations if van der Waals effects are included. Resonant XES can be used to distinguish two different species of CO on the surface; vibrationally hot, chemisorbed CO and CO in the precursor state. Laser-induced CO oxidation on Ru(0001) is modeled and three competing mechanisms are found. Kinetic modeling reproduces the experiment qualitatively.

  • 11.
    Öberg, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Anniyev, Toyli
    Vojvodic, Aleksandra
    Kaya, Sarp
    Ogasawara, Hirohito
    Friebel, Daniel
    Miller, Daniel J.
    Nordlund, Dennis
    Bergmann, Uwe
    Ljungberg, Mathias P.
    Stockholm University, Faculty of Science, Department of Physics.
    Abild-Pedersen, Frank
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics. SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, Menlo Pk, CA 94025 USA.
    Pettersson, Lars G.M.
    Stockholm University, Faculty of Science, Department of Physics.
    Stability of Pt-Modified Cu(111) in the Presence of Oxygen and Its Implication on the Overall Electronic Structure2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 32, p. 16371-16380Article in journal (Refereed)
    Abstract [en]

    The electronic structure and stability of Cu(111)-hosted Pt overlayers with and without the presence of atomic oxygen have been studied by means of core-level spectroscopy and density functional theory (DFT). Because of lattice mismatch, Pt(111) overlayers grown on Cu(111) are compressively strained, and hard X-ray photoelectron spectroscopy together with Pt L-3-edge X-ray absorption spectroscopy (XAS) reveals a pronounced downshift of the Pt d-band owing to the increased overlap of the d-orbitals, an effect also reproduced theoretically. Exposure to oxygen severely alters the surface composition; the O-Cu binding energy largely exceeds that of O-Pt, and DFT calculations predict surface segregation of Cu atoms. Comparing the adsorbate electronic structure for O on unstrained Pt(111) with that of O on Pt-modified Cu(111) using O K-edge XAS and X-ray emission spectroscopy salient differences are observed and calculations show that Cu-segregation to the topmost layer is required to reproduce the measured spectra. It is proposed that O is binding in a hollow site constituted by at least two Cu atoms and that up to 75% of the Pt atoms migrate below the surface.

  • 12.
    Öberg, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gladh, Jörgen
    Stockholm University, Faculty of Science, Department of Physics.
    Dell'Angela, M.
    Anniyev, T.
    Beye, M.
    Coffee, R.
    Föhlisch, A.
    Katayama, T.
    Kaya, S.
    LaRue, J.
    Mögelhöj, A.
    Nordlund, D.
    Ogasawara, H.
    Schlotter, W. F.
    Sellberg, Jonas A.
    Stockholm University, Faculty of Science, Department of Physics. SLAC National Accelerator Laboratory, USA.
    Sorgenfrei, F.
    Turner, J. J.
    Wolf, M.
    Wurth, W.
    Öström, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics. SLAC National Accelerator Laboratory, USA.
    Nörskov, J. K.
    Pettersson, L. G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Optical laser-induced CO desorption from Ru(0001) monitored with a free-electron X-ray laser: DFT prediction and X-ray confirmation of a precursor state2015In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 640, p. 80-88Article in journal (Refereed)
    Abstract [en]

    We present density functional theory modeling of time-resolved optical pump/X-ray spectroscopic probe data of CO desorption from Ru(0001). The BEEF van der Waals functional predicts a weakly bound state as a precursor to desorption. The optical pump leads to a near-instantaneous (<100 fs) increase of the electronic temperature to nearly 7000 K. The temperature evolution and energy transfer between electrons, substrate phonons and adsorbate is described by the two-temperature model and found to equilibrate on a timescale of a few picoseconds to an elevated local temperature of similar to 2000K. Estimating the free energy based on the computed potential of mean force along the desorption path, we find an entropic barrier to desorption (and by time-reversal also to adsorption). This entropic barrier separates the chemisorbed and precursor states, and becomes significant at the elevated temperature of the experiment (similar to 1.4 eV at 2000 K). Experimental pump-probe X-ray absorption/X-ray emission spectroscopy indicates population of a precursor state to desorption upon laser-excitation of the system (Dell'Angela et al., 2013). Computing spectra along the desorption path confirms the picture of a weakly bound transient state arising from ultrafast heating of the metal substrate.

  • 13.
    Öberg, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gladh, Jörgen
    Stockholm University, Faculty of Science, Department of Physics.
    Marks, Kess
    Stockholm University, Faculty of Science, Department of Physics.
    Ogasawara, H.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics. SLAC National Accelerator Laboratory, USA.
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Östrom, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Indication of non-thermal contribution to visible femtosecond laser-induced CO oxidation on Ru(0001)2015In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 143, no 7, article id 074701Article in journal (Refereed)
    Abstract [en]

    We studied CO oxidation on Ru(0001) induced by 400 nm and 800 nm femtosecond laser pulses where we find a branching ratio between CO oxidation and desorption of 1: 9 and 1: 31, respectively, showing higher selectivity towards CO oxidation for the shorter wavelength excitation. Activation energies computed with density functional theory show discrepancies with values extracted from the experiments, indicating both a mixture between different adsorbed phases and importance of non-adiabatic effects on the effective barrier for oxidation. We simulated the reactions using kinetic modeling based on the two-temperature model of laser-induced energy transfer in the substrate combined with a friction model for the coupling to adsorbate vibrations. This model gives an overall good agreement with experiment except for the substantial difference in yield ratio between CO oxidation and desorption at 400 nm and 800 nm. However, including also the initial, non-thermal effect of electrons transiently excited into antibonding states of the O-Ru bond yielded good agreement with all experimental results.

  • 14.
    Öberg, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gladh, Jörgen
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, Lars G M
    Stockholm University, Faculty of Science, Department of Physics.
    Öström, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    CO oxidation on Ru(0001) modeled from first-principles and femtosecond laser measurementsManuscript (preprint) (Other academic)
  • 15.
    Öberg, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Nestsiarenka, Yuliya
    Stockholm University, Faculty of Science, Department of Physics.
    Matsuda, A.
    Stockholm University, Faculty of Science, Department of Physics.
    Gladh, Jörgen
    Stockholm University, Faculty of Science, Department of Physics.
    Hansson, Tony
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, Lars G.M.
    Stockholm University, Faculty of Science, Department of Physics.
    Öström, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Adsorption and Cyclotrimerization Kinetics of C2H2 at a Cu(110) Surface2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 17, p. 9550-9560Article in journal (Refereed)
    Abstract [en]

    The kinetics of acetylene adsorption and cyclotrimerization was studied by vibrational sum-frequency generation spectroscopy (SFG) and density functional theory (DFT) calculations. At low temperature, SFG shows two resonances corresponding to acetylene adsorbed in two different sites. Upon heating, two new vibrational resonances appear. We interpret these resonances as being due to C2H2 island formation and adsorbed C4H4, which is the intermediate in the subsequent cyclotrimerization reaction to form benzene. A kinetic model is applied, which allows determination of the relevant activation barriers. The barrier for C2H2 diffusion is determined to be 43 +/- 1 kJ/mol. The activation barrier for formation of the C4H4 intermediate is found to be 84 +/- 6 kJ/mol and the barrier for benzene formation 5 +/- 3 kJ/mol lower. Barriers to diffusion and formation of C4H4 and C6H6 obtained from DFT calculations are in quantitative agreement with the experiments once the locally high coverage in C2H2 islands is included.

  • 16.
    Östrom, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Öberg, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Xin, H.
    Larue, J.
    Beye, M.
    Dell'Angela, M.
    Gladh, Jörgen
    Stockholm University, Faculty of Science, Department of Physics.
    Ng, M. L.
    Sellberg, Jonas A.
    Stockholm University, Faculty of Science, Department of Physics. SLAC National Accelerator Laboratory, USA.
    Kaya, S.
    Mercurio, G.
    Nordlund, D.
    Hantschmann, M.
    Hieke, F.
    Kuehn, D.
    Schlotter, W. F.
    Dakovski, G. L.
    Turner, J. J.
    Minitti, M. P.
    Mitra, A.
    Moeller, S. P.
    Foehlisch, A.
    Wolf, M.
    Wurth, W.
    Persson, M.
    Norskov, J. K.
    Abild-Pedersen, F.
    Ogasawara, H.
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics. SLAC National Accelerator Laboratory, USA.
    Probing the transition state region in catalytic CO oxidation on Ru2015In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 347, no 6225, p. 978-982Article in journal (Refereed)
    Abstract [en]

    Femtosecond x-ray laser pulses are used to probe the carbon monoxide (CO) oxidation reaction on ruthenium (Ru) initiated by an optical laser pulse. On a time scale of a few hundred femtoseconds, the optical laser pulse excites motions of CO and oxygen (O) on the surface, allowing the reactants to collide, and, with a transient close to a picosecond (ps), new electronic states appear in the OK-edge x-ray absorption spectrum. Density functional theory calculations indicate that these result from changes in the adsorption site and bond formation between CO and O with a distribution of OC-O bond lengths close to the transition state (TS). After 1 ps, 10% of the CO populate the TS region, which is consistent with predictions based on a quantum oscillator model.

1 - 16 of 16
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf