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  • 1. Aquilante, Francesco
    et al.
    Autschbach, Jochen
    Baiardi, Alberto
    Battaglia, Stefano
    Borin, Veniamin A.
    Chibotaru, Liviu F.
    Conti, Irene
    De Vico, Luca
    Delcey, Mickael
    Galvan, Ignacio Fdez.
    Ferre, Nicolas
    Freitag, Leon
    Garavelli, Marco
    Gong, Xuejun
    Knecht, Stefan
    Larsson, Ernst D.
    Lindh, Roland
    Lundberg, Marcus
    Malmqvist, Per Ake
    Nenov, Artur
    Norell, Jesper
    Stockholm University, Faculty of Science, Department of Physics.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Olivucci, Massimo
    Pedersen, Thomas B.
    Pedraza-Gonzalez, Laura
    Phung, Quan M.
    Pierloot, Kristine
    Reiher, Markus
    Schapiro, Igor
    Segarra-Marti, Javier
    Segatta, Francesco
    Seijo, Luis
    Sen, Saumik
    Sergentu, Dumitru-Claudiu
    Stein, Christopher J.
    Ungur, Liviu
    Vacher, Morgane
    Valentini, Alessio
    Veryazov, Valera
    Modern quantum chemistry with [Open]Molcas2020In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 152, no 21, article id 214117Article in journal (Refereed)
    Abstract [en]

    MOLCAS/OpenMolcas is an ab initio electronic structure program providing a large set of computational methods from Hartree-Fock and density functional theory to various implementations of multiconfigurational theory. This article provides a comprehensive overview of the main features of the code, specifically reviewing the use of the code in previously reported chemical applications as well as more recent applications including the calculation of magnetic properties from optimized density matrix renormalization group wave functions.

  • 2.
    Banerjee, Ambar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Coates, Michael R.
    Stockholm University, Faculty of Science, Department of Physics.
    Kowalewski, Markus
    Stockholm University, Faculty of Science, Department of Physics.
    Wikmark, Hampus
    Jay, Raphael M.
    Wernet, Philippe
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Photoinduced bond oscillations in ironpentacarbonyl give delayed synchronous bursts of carbonmonoxide release2022In: Nature Communications, E-ISSN 2041-1723, Vol. 13, no 1, article id 1337Article in journal (Refereed)
    Abstract [en]

    Early excited state dynamics in the photodissociation of transition metal carbonyls determines the chemical nature of short-lived catalytically active reaction intermediates. However, time-resolved experiments have not yet revealed mechanistic details in the sub-picosecond regime. Hence, in this study the photoexcitation of ironpentacarbonyl Fe(CO)5 is simulated with semi-classical excited state molecular dynamics. We find that the bright metal-to-ligand charge-transfer (MLCT) transition induces synchronous Fe-C oscillations in the trigonal bipyramidal complex leading to periodically reoccurring release of predominantly axial CO. Metaphorically the photoactivated Fe(CO)5 acts as a CO geyser, as a result of dynamics in the potential energy landscape of the axial Fe-C distances and non-adiabatic transitions between manifolds of bound MLCT and dissociative metal-centered (MC) excited states. The predominant release of axial CO ligands and delayed release of equatorial CO ligands are explained in a unified mechanism based on the σ*(Fe-C) anti-bonding character of the receiving orbital in the dissociative MC states.

  • 3.
    Banerjee, Ambar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Coates, Michael R.
    Stockholm University, Faculty of Science, Department of Physics.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Spectroscopic Signature of Dynamical Instability of the Aqueous Complex in the Brown-Ring Nitrate Test2022In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 28, no 54, article id e202200923Article in journal (Refereed)
    Abstract [en]

    The chemistry of the brown-ring test has been investigated for nearly a century. Though recent studies have focused on solid state structure determination and measurement of spectra, mechanistic details and kinetics, the aspects of solution structure and dynamics remain unknown. We have studied structural fluctuations of the brown-ring complex in aqueous solution with ab-initio molecular dynamics simulations, from which we identified that the classically established pseudo-octahedral [Fe(H2O)5(NO)]2+ complex is present along with a square-pyramidal [Fe(H2O)4(NO)]2+ complex. Based on the inability in multi-reference calculations to reproduce the experimental UV-vis spectra in aqueous solution by inclusion of thermal fluctuations of the [Fe(H2O)5(NO)]2+ complex alone, we propose the existence of an equilibrium between pseudo-octahedral and square-pyramidal complexes. Despite challenges in constructing models reproducing the solid-state UV-vis spectrum, the advanced spectrum simulation tool motivates us to challenge the established picture of a sole pseudo-octahedral complex in solution. 

  • 4.
    Banerjee, Ambar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    da Cruz, Vinicius Vaz
    Ekholm, Victor
    Sathe, Conny
    Rubensson, Jan-Erik
    Ignatova, Nina
    Gel'mukhanov, Faris
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Simulating fluorine K-edge resonant inelastic x-ray scattering of sulfur hexafluoride and the effect of dissociative dynamics2023In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 108, no 2, article id 023103Article in journal (Refereed)
    Abstract [en]

    We report on a computational study of resonant inelastic x-ray scattering (RIXS), at different fluorine K-edge resonances of the SF6 molecule, and corresponding nonresonant x-ray emission. Previously measured polarization dependence in RIXS is reproduced and traced back to the local sigma and pi symmetry of the molecular orbitals and corresponding states involved in the RIXS process. Also electron-hole coupling energies are calculated and related to experimentally observed spectator shifts. The role of dissociative S-F bond dynamics is explored to model detuning of RIXS spectra at the |F1s(-1) 6a(1g)(1)> resonance, which shows challenges to accurately reproduce the required steepness for core-excited potential energy surface. We show that the RIXS spectra can only be properly described by considering breaking of the global inversion symmetry of the electronic wave function and core-hole localization, induced by vibronic coupling. Due to the core-hole localization we have symmetry forbidden transitions, which lead to additional resonances and changing width of the RIXS profile.

  • 5. Banerjee, Ambar
    et al.
    Jay, Raphael M.
    Leitner, Torsten
    Wang, Ru-Pan
    Harich, Jessica
    Stefanuik, Robert
    Coates, Michael R.
    Stockholm University, Faculty of Science, Department of Physics.
    Beale, Emma V.
    Kabanova, Victoria
    Kahraman, Abdullah
    Wach, Anna
    Ozerov, Dmitry
    Arrell, Christopher
    Milne, Christopher
    Johnson, Philip J. M.
    Cirelli, Claudio
    Bacellar, Camila
    Huse, Nils
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Wernet, Philippe
    Accessing metal-specific orbital interactions in C–H activation with resonant inelastic X-ray scattering2024In: Chemical Science, ISSN 2041-6520, E-ISSN 2041-6539, Vol. 15, no 7, p. 2398-2409Article in journal (Refereed)
    Abstract [en]

    Photochemically prepared transition-metal complexes are known to be effective at cleaving the strong C–H bonds of organic molecules in room temperature solutions. There is also ample theoretical evidence that the two-way, metal to ligand (MLCT) and ligand to metal (LMCT), charge-transfer between an incoming alkane C–H group and the transition metal is the decisive interaction in the C–H activation reaction. What is missing, however, are experimental methods to directly probe these interactions in order to reveal what determines reactivity of intermediates and the rate of the reaction. Here, using quantum chemical simulations we predict and propose future time-resolved valence-to-core resonant inelastic X-ray scattering (VtC-RIXS) experiments at the transition metal L-edge as a method to provide a full account of the evolution of metal–alkane interactions during transition-metal mediated C–H activation reactions. For the model system cyclopentadienyl rhodium dicarbonyl (CpRh(CO)2), we demonstrate, by simulating the VtC-RIXS signatures of key intermediates in the C–H activation pathway, how the Rh-centered valence-excited states accessible through VtC-RIXS directly reflect changes in donation and back-donation between the alkane C–H group and the transition metal as the reaction proceeds via those intermediates. We benchmark and validate our quantum chemical simulations against experimental steady-state measurements of CpRh(CO)2 and Rh(acac)(CO)2 (where acac is acetylacetonate). Our study constitutes the first step towards establishing VtC-RIXS as a new experimental observable for probing reactivity of C–H activation reactions. More generally, the study further motivates the use of time-resolved VtC-RIXS to follow the valence electronic structure evolution along photochemical, photoinitiated and photocatalytic reactions with transition metal complexes.

  • 6. Bednarska, Joanna
    et al.
    Zalesny, Robert
    Murugan, N. Arul
    Bartkowiak, Wojciech
    Agren, Hans
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Elucidating the Mechanism of Zn2+ Sensing by a Bipyridine Probe Based on Two-Photon Absorption2016In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 120, no 34, p. 9067-9075Article in journal (Refereed)
    Abstract [en]

    In this work, we examine, by means of computational methods, the mechanism of Zn2+ sensing by a bipyridine-centered, D-pi-A-pi-D-type-ratiometric molecular probe. According to recently published experimental data [Divya, K. P.; Sreejith, S.; Ashokkumar, P.; Yuzhan, K.; Peng, Q; Maji, S. K.; Tong, Y.; Yu, H.; Zhao, Y.; Ramamurthy, P.; Ajayaghosh, A. A ratiometric fluorescent molecular -probe with enhanced two-photon response upon Zn2+ binding for in vitro and in vivo: bioimaging.= Chem. Sci. 2014, S, 3469-3474], after coordination to zinc ions the -probe exhibits a large enhancement of the two -photon absorption cross section. The goal of our investigation was to elucidate the mechanism behind this phenomenon. For this purpose, linear and nonlinear optical properties of -the unbound (cation-free) and bound probe were calculated, including the influence of solute Solvent interactions, implicitly using a polarizable continuum model and exp-licitely employing the QM/MM approach. Because the results of the calculations indicate that many conformers of the probe are energetically accessible at room temperature in solution and hence contribute to the Signal, structurepteperty relationships were also taken into account. Results of our simulations-demonstrate that the one-photon absorption bands for both the unbound -and bound forms correspond to the bright pi -> pi* transition to the first excited state; which, on the other hand,. exhibits negligible two-photon activity. On the basis of the results of the quadratic respOnse calculations, we put forward-notion that it is the second excited state that gives the strong signal in the experimental nonlinear spectrum. To explain the differenCes in the two-photon absorption activity for the two lowest-lying excited states and nonlinear response enhancement upon binding, we employed the generalized few -state model including the ground, first, and- second excited states. The analysis of the optical channel suggests that the large two-photon response is due to the coordination -induced increase of the, transition- moment from the first to the second excited state.

  • 7. Blum, M.
    et al.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Weinhardt, L.
    Pookpanratana, S.
    Baer, M.
    Zhang, Y.
    Fuchs, O.
    Yang, W.
    Umbach, E.
    Heske, C.
    Ultrafast Proton Dynamics in Aqueous Amino Acid Solutions Studied by Resonant Inelastic Soft X-ray Scattering2012In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 116, no 46, p. 13757-13764Article in journal (Refereed)
    Abstract [en]

    Resonant inelastic soft X-ray scattering (RIXS) has been used to study the electronic structure of glycine and lysine in aqueous solution. Upon variation of the pH value of the solution from acidic to basic, major changes of the nitrogen K edge RIXS data are observed for both amino acids, which are associated with the protonation and deprotonation of the amino groups. The experimental results are compared with simulations based on density functional theory, yielding a detailed understanding of the spectral changes, as well as insights into the ultrafast proton dynamics in the intermediate core-excited/ionized state of the RIXS process.

  • 8.
    Cavalleri, M.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Nordlund, D.
    Stockholm University, Faculty of Science, Department of Physics.
    Odelius, M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, A.
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, L.G.M.
    Stockholm University, Faculty of Science, Department of Physics.
    Half or full core hole in density functional theory X-ray absorption spectrum calculations of water?2005In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 7, no 15, p. 2854-2858Article in journal (Refereed)
    Abstract [en]

    We analyze the performance of two different core-hole potentials in the theoretical modeling of XAS of ice, liquid and gas phase water; the use of a full core-hole (FCH) in the calculations, as suggested by Hetenyi et al. [B. Hetenyi, F. De Angelis, P. Giamozzi and R. Car, J. Chem. Phys., 2004, 120(18), 8632], gives poor agreement with experiment in terms of intensity distribution as well as transition energies, while the half core hole (HCH) potential, in the case of water, provides a better compromise between initial and final state effects, leading to good agreement with the experimental data.

  • 9. Chaudhuri, A
    et al.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Jones, R G
    Lee, T-L
    Detlefs, B
    Woodruff, D P
    The structure of the Au(111)/methylthiolate interface: new insights from near-edge x-ray absorption spectroscopy and x-ray standing waves.2009In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 130, no 12, p. 124708-Article in journal (Refereed)
    Abstract [en]

    The local structure of the Au(111)(√3x√3)R30 degrees-methylthiolate surface phase has been investigated by S K-edge near-edge s-ray absorption fine structure (NEXAFS) both experimentally and theoretically and by experimental normal-incidence x-ray standing waves (NIXSW) at both the C and S atomic sites. NEXAFS shows not only excitation into the intramolecular σ*S-C resonance but also into a σ* S-Au orbital perpendicular to the surface, clearly identifying the local S headgroup site as atop a Au atom. Simulations show that it is not possible, however, to distinguish between the two possible adatom reconstruction models; a single thiolate species atop a hollow-site Au adatom or a dithiolate moiety comprising two thiolate species bonded to a bridge-bonded Au adatom. Within this dithiolate moiety a second σ* S-Au orbital that lies near parallel to the surface has a higher energy that overlaps that of the σ* S-C resonance. The new NIXSW data show the S-C bond to be tilted by 61 degrees relative to the surface normal, with a preferred azimuthal orientation in <211>, corresponding to the intermolecular nearest-neighbor directions. This azimuthal orientation is consistent with the thiolate being atop a hollow-site Au adatom, but not consistent with the originally proposed Au-adatom-dithiolate moiety. However, internal conformational changes within this species could, perhaps, render this model also consistent with the experimental data.

  • 10.
    Coates, Michael R.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Banerjee, Ambar
    Stockholm University, Faculty of Science, Department of Physics.
    Jay, Raphael M.
    Wernet, Philippe
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Theoretical Investigation of Transient Species Following Photodissociation of Ironpentacarbonyl in Ethanol Solution2024In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 63, no 23, p. 10634-10647Article in journal (Refereed)
    Abstract [en]

    Photodissociation of ironpentacarbonyl [Fe-1(CO)(5)] in solution generates transient species in different electronic states, which we studied theoretically. From ab initio molecular dynamics simulations in ethanol solution, the closed-shell parent compound Fe-1(CO)(5) is found to interact weakly with the solvent, whereas the irontetracarbonyl [Fe(CO)(4)] species, formed after photodissociation, has a strongly spin-dependent behavior. It coordinates a solvent molecule tightly in the singlet state [Fe-1(CO)(4)] and weakly in the triplet state [Fe-3(CO)(4)]. From the simulations, we have gained insights into intersystem crossing in solvated irontetracarbonyl based on the distinct structural differences induced by the change in multiplicity. Alternative forms of coordination between Fe-1(CO)(4) and functional groups of the ethanol molecule are simulated, and a quantum chemical investigation of the energy landscape for the coordinated irontetracarbonyl gives information about the interconversion of different transient species in solution. Furthermore, insights from the simulations, in which we find evidence of a solvent exchange mechanism, challenge the previously proposed mechanism of chain walking for under-coordinated metal carbonyls in solution.

  • 11.
    Coates, Michael R.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Banerjee, Ambar
    Stockholm University, Faculty of Science, Department of Physics.
    Jay, Raphael M.
    Uppsala Universitet.
    Wernet, Philippe
    Uppsala Universitet.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Theoretical Investigation of Transient Speciesfollowing Photodissociation of Ironpentacarbonylin Ethanol SolutionManuscript (preprint) (Other academic)
    Abstract [en]

    Photodissociation of ironpentacarbonyl in solution generates transient species indifferent electronic states, which we have studied theoretically. From ab initio moleculardynamics simulations in ethanol solutions, the close-shell parent compound 1Fe(CO)5 is found to interact weakly with the solvent, whereas the irontetracarbonyl species,formed after photodissociation, has a strongly spin-dependent behavior. It coordinatesa solvent molecule tightly in the singlet state (1Fe(CO)4) and weakly in the tripletstate (3Fe(CO)4). Alternative forms of coordination between 1Fe(CO)4 and functionalgroups of the ethanol molecule are simulated, and quantum chemical calculations ofthe energy landscape for the coordinated irontetracarbonyl give information aboutthe inter-conversion of different transient species in solution. Furthermore, insights1from the simulations challenge the previously proposed mechanism of chain walkingfor undercoordinate metal carbonyls in solution. Thereby, we gain insight into bothintersystem crossing in solvated irontetracarbonyl and its exchange in coordinationbetween Fe−OH and Fe−HC.

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  • 12.
    Coates, Michael R.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Banerjee, Ambar
    Stockholm University, Faculty of Science, Department of Physics.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Simulations of the Aqueous Brown-Ring Complex Reveal Fluctuations in Electronic Character2023In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 62, p. 16854-16866Article in journal (Refereed)
    Abstract [en]

    Ab initio molecular dynamics (AIMD) simulations of the aqueous [Fe(H2O)(5)(NO)](2+) brown-ring complex in different spin states, in combination with multiconfigurational quantum chemical calculations, show a structural dependence on the electronic character of the complex. Sampling in the quartet and sextet ground states show that the multiplicity is correlated with the Fe-N distance. This provides a motivation for a rigid Fe-N scan in the isolated brown-ring complex to investigate how the multiconfigurational wave function and the electron density change around the FeNO moiety. Our results show that subtle changes in the Fe-N distance produce a large response in the electronic configurations underlying the quartet wave function. However, while changes in spin density and potential energy are pronounced, variations in charge are negligible. These trends within the FeNO moiety are preserved in structural sampling of the AIMD simulations, despite distortions present in other degrees of freedom in the bulk solution.

  • 13. Couto, Rafael C.
    et al.
    Cruz, Vinicius V.
    Ertan, Emelie
    Stockholm University, Faculty of Science, Department of Physics.
    Eckert, Sebastian
    Fondell, Mattis
    Dantz, Marcus
    Kennedy, Brian
    Schmitt, Thorsten
    Pietzsch, Annette
    Guimarães, Freddy F.
    Ågren, Hans
    Gel'mukhanov, Faris
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Kimberg, Victor
    Föhlisch, Alexander
    Selective gating to vibrational modes through resonant X-ray scattering2017In: Nature Communications, E-ISSN 2041-1723, Vol. 8, article id 14165Article in journal (Refereed)
    Abstract [en]

    The dynamics of fragmentation and vibration of molecular systems with a large number of coupled degrees of freedom are key aspects for understanding chemical reactivity and properties. Here we present a resonant inelastic X-ray scattering (RIXS) study to show how it is possible to break down such a complex multidimensional problem into elementary components. Local multimode nuclear wave packets created by X-ray excitation to different core-excited potential energy surfaces (PESs) will act as spatial gates to selectively probe the particular ground-state vibrational modes and, hence, the PES along these modes. We demonstrate this principle by combining ultra-high resolution RIXS measurements for gas-phase water with state-of-the-art simulations.

  • 14. da Cruz, Vinícius Vaz
    et al.
    Gel'mukhanov, Faris
    Eckert, Sebastian
    Iannuzzi, Marcella
    Ertan, Emelie
    Stockholm University, Faculty of Science, Department of Physics.
    Pietzsch, Annette
    Couto, Rafael C.
    Niskanen, Johannes
    Fondell, Mattis
    Dantz, Marcus
    Schmitt, Thorsten
    Lu, Xingye
    McNally, Daniel
    Jay, Raphael M.
    Kimberg, Victor
    Föhlisch, Alexander
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Probing hydrogen bond strength in liquid water by resonant inelastic X-ray scattering2019In: Nature Communications, E-ISSN 2041-1723, Vol. 10, article id 1013Article in journal (Refereed)
    Abstract [en]

    Local probes of the electronic ground state are essential for understanding hydrogen bonding in aqueous environments. When tuned to the dissociative core-excited state at the O1s pre-edge of water, resonant inelastic X-ray scattering back to the electronic ground state exhibits a long vibrational progression due to ultrafast nuclear dynamics. We show how the coherent evolution of the OH bonds around the core-excited oxygen provides access to high vibrational levels in liquid water. The OH bonds stretch into the long-range part of the potential energy curve, which makes the X-ray probe more sensitive than infra-red spectroscopy to the local environment. We exploit this property to effectively probe hydrogen bond strength via the distribution of intramolecular OH potentials derived from measurements. In contrast, the dynamical splitting in the spectral feature of the lowest valence-excited state arises from the short-range part of the OH potential curve and is rather insensitive to hydrogen bonding.

  • 15. da Cruz, Vinícius Vaz
    et al.
    Ignatova, Nina
    Couto, Rafael C.
    Fedotov, Daniil A.
    Rehn, Dirk R.
    Savchenko, Viktoriia
    Norman, Patrick
    Ågren, Hans
    Polyutov, Sergey
    Niskanen, Johannes
    Eckert, Sebastian
    Jay, Raphael M.
    Fondell, Mattis
    Schmitt, Thorsten
    Pietzsch, Annette
    Föhlisch, Alexander
    Gel'mukhanov, Faris
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Kimberg, Victor
    Nuclear dynamics in resonant inelastic X-ray scattering and X-ray absorption of methanol2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, no 23, article id 234301Article in journal (Refereed)
    Abstract [en]

    We report on a combined theoretical and experimental study of core-excitation spectra of gas and liquid phase methanol as obtained with the use of X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS). The electronic transitions are studied with computational methods that include strict and extended second-order algebraic diagrammatic construction [ADC(2) and ADC(2)-x], restricted active space second-order perturbation theory, and time-dependent density functional theory-providing a complete assignment of the near oxygen K-edge XAS. We show that multimode nuclear dynamics is of crucial importance for explaining the available experimental XAS and RIXS spectra. The multimode nuclear motion was considered in a recently developed mixed representation where dissociative states and highly excited vibrational modes are accurately treated with a time-dependent wave packet technique, while the remaining active vibrational modes are described using Franck-Condon amplitudes. Particular attention is paid to the polarization dependence of RIXS and the effects of the isotopic substitution on the RIXS profile in the case of dissociative core-excited states. Our approach predicts the splitting of the 2a RIXS peak to be due to an interplay between molecular and pseudo-atomic features arising in the course of transitions between dissociative core- and valence-excited states. The dynamical nature of the splitting of the 2a peak in RIXS of liquid methanol near pre-edge core excitation is shown. The theoretical results are in good agreement with our liquid phase measurements and gas phase experimental data available from the literature.

  • 16.
    Das, Sambit Kumar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Banerjee, Ambar
    Stockholm University, Faculty of Science, Department of Physics. Uppsala University, Sweden.
    Simulating non-adiabatic dynamics of photoexcited phenyl azide: Investigating electronic and structural relaxation en route to the formation of phenyl nitrene2024In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 30, no 7, article id e202302178Article in journal (Refereed)
    Abstract [en]

    Excited state molecular dynamics simulations of the photoexcited phenyl azide have been performed. The semi-classical surface hopping approximation has enabled an unconstrained analysis of the electronic and nuclear degrees of freedom which contribute to the molecular dissociation of phenyl azide into phenyl nitrene and molecular nitrogen. The significance of the second singlet excited state in leading the photodissociation has been established through electronic structure calculations, based on multi-configurational schemes, and state population dynamics. The investigations on the structural dynamics have revealed the NN bond separation to be accompanied by synchronous changes in the azide NNN bond angle. The 100 fs simulation results in a nitrene fragment that is electronically excited in the singlet manifold.

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  • 17.
    Das, Sambit Kumar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Winghart, Marc-Oliver
    Han, Peng
    Rana, Debkumar
    Zhang, Zhuang-Yan
    Eckert, Sebastian
    Fondell, Mattis
    Schnappinger, Thomas
    Stockholm University, Faculty of Science, Department of Physics.
    Nibbering, Erik T. J.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Electronic Fingerprint of the Protonated Imidazole Dimer Probed by X-ray Absorption Spectroscopy2024In: The Journal of Physical Chemistry Letters, E-ISSN 1948-7185, Vol. 15, no 5, p. 1264-1272Article in journal (Refereed)
    Abstract [en]

    Protons in low-barrier superstrong hydrogen bonds are typically delocalized between two electronegative atoms. Conventional methods to characterize such superstrong hydrogen bonds are vibrational spectroscopy and diffraction techniques. We introduce soft X-ray spectroscopy to uncover the electronic fingerprints for proton sharing in the protonated imidazole dimer, a prototypical building block enabling effective proton transport in biology and high-temperature fuel cells. Using nitrogen core excitations as a sensitive probe for the protonation status, we identify the X-ray signature of a shared proton in the solvated imidazole dimer in a combined experimental and theoretical approach. The degree of proton sharing is examined as a function of structural variations that modify the shape of the low-barrier potential in the superstrong hydrogen bond. We conclude by showing how the sensitivity to the quantum distribution of proton motion in the double-well potential is reflected in the spectral signature of the shared proton. 

  • 18.
    Das, Sambit
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Banerjee, Ambar
    Stockholm University, Faculty of Science, Department of Physics.
    Theoretical simulations of the photodissociation of phenyl azideManuscript (preprint) (Other academic)
    Abstract [en]

    Excited state molecular dynamics simulations of the photoexcitation of phenyl azide have been performed. The semi-classical surface hopping approximation has enabled an unconstrained analysis of the electronic and nuclear degrees of freedom which contribute to the molecular dissociation of phenyl azide into phenyl nitrene and molecular nitrogen. The significance of the S2 state in leading the photodissociation has been established through electronic structure calculations, based on multiconfigurational schemes, and state population dynamics. The investigations on the structural dynamics have revealed the N-N bond separation to be accompanied by synchronous changes in the azide N-N-N bond angle. The 100 fs simulation results in a nitrene fragment that is electronically and vibrationally excited, thus forming a hot nitrene species in the singlet manifold.

  • 19.
    Das, Sambit
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Nibbering, Erik
    MAX BORN INSTITUTE for Nonlinear Optics and Short Pulse Spectroscopy.
    Zhang, Zhuang-Yan
    MAX BORN INSTITUTE for Nonlinear Optics and Short Pulse Spectroscopy.
    Winghart, Marc-Oliver
    MAX BORN INSTITUTE for Nonlinear Optics and Short Pulse Spectroscopy.
    Probing the electronic structure of imidazole complexes in solution with quantum chemistry and X-ray absorption spectroscopyManuscript (preprint) (Other academic)
    Abstract [en]

    By combing soft X-ray spectroscopy and theoretical calculations, characterization of the shared proton in the imidazole molecular complex has been done. With nitrogen core-level excitations as a sensitive reporter about the protonation status, a new absorption resonance is observed at a pH where exactly half of the imidazoles are protonated, right between the known absorptions of pure imidazole and pure imidazolium. Supported by TDDFT calculations, the spectral signature has been assigned to the sharing of the excess proton between two imidazole molecules in an asymmetric double minimum potential. Analysis of the discrete core excitations reveals shared electronic attributes between the molecular complex and individual monomers. The theoretical investigation also uncovers the influence of the shared proton on the intrinsic features and the overall spectral outcome.

  • 20. de Groot, Frank M. F.
    et al.
    Elnaggar, Hebatalla
    Frati, Federica
    Wang, Ru-pan
    Delgado-Jaime, Mario U.
    van Veenendaal, Michel
    Fernandez-Rodriguez, Javier
    Haverkort, Maurits W.
    Green, Robert J.
    van der Laan, Gerrit
    Kvashnin, Yaroslav
    Hariki, Atsushi
    Ikeno, Hidekazu
    Ramanantoanina, Harry
    Daul, Claude
    Delley, Bernard
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Lundberg, Marcus
    Kuhn, Oliver
    Bokarev, Sergey
    Shirley, Eric
    Vinson, John
    Gilmore, Keith
    Stener, Mauro
    Fronzoni, Giovanna
    Decleva, Piero
    Kruger, Peter
    Retegan, Marius
    Joly, Yves
    Vorwerk, Christian
    Draxl, Claudia
    Rehr, John
    Tanaka, Arata
    2p x-ray absorption spectroscopy of 3d transition metal systems2021In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 249, article id 147061Article in journal (Refereed)
    Abstract [en]

    This review provides an overview of the different methods and computer codes that are used to interpret 2p x-ray absorption spectra of 3d transition metal ions. We first introduce the basic parameters and give an overview of the methods used. We start with the semi-empirical multiplet codes and compare the different codes that are available. A special chapter is devoted to the user friendly interfaces that have been written on the basis of these codes. Next we discuss the first principle codes based on band structure, including a chapter on Density Functional theory based approaches. We also give an overview of the first-principle multiplet codes that start from a cluster calculation and we discuss the wavefunction based methods, including multi-reference methods. We end the review with a discussion of the link between theory and experiment and discuss the open issues in the spectral analysis.

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  • 21. Eckert, Sebastian
    et al.
    da Cruz, Vinícius Vaz
    Gel'mukhanov, Faris
    Ertan, Emelie
    Stockholm University, Faculty of Science, Department of Physics.
    Ignatova, Nina
    Polyutov, Sergey
    Couto, Rafael C.
    Fondell, Mattis
    Dantz, Marcus
    Kennedy, Brian
    Schmitt, Thorsten
    Pietzsch, Annette
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Föhlisch, Alexander
    One-dimensional cuts through multidimensional potential-energy surfaces by tunable x rays2018In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 97, no 5, article id 053410Article in journal (Refereed)
    Abstract [en]

    The concept of the potential-energy surface (PES) and directional reaction coordinates is the backbone of our description of chemical reaction mechanisms. Although the eigenenergies of the nuclear Hamiltonian uniquely link a PES to its spectrum, this information is in general experimentally inaccessible in large polyatomic systems. This is due to (near) degenerate rovibrational levels across the parameter space of all degrees of freedom, which effectively forms a pseudospectrum given by the centers of gravity of groups of close-lying vibrational levels. We show here that resonant inelastic x-ray scattering (RIXS) constitutes an ideal probe for revealing one-dimensional cuts through the ground-state PES of molecular systems, even far away from the equilibrium geometry, where the independent-mode picture is broken. We strictly link the center of gravity of close-lying vibrational peaks in RIXS to a pseudospectrum which is shown to coincide with the eigenvalues of an effective one-dimensional Hamiltonian along the propagation coordinate of the core-excited wave packet. This concept, combined with directional and site selectivity of the core-excited states, allows us to experimentally extract cuts through the ground-state PES along three complementary directions for the showcase H2O molecule.

  • 22. Eckert, Sebastian
    et al.
    Norell, Jesper
    Stockholm University, Faculty of Science, Department of Physics.
    Jay, Raphael M.
    Fondell, Mattis
    Mitzner, Rolf
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Föhlisch, Alexander
    T-1 Population as the Driver of Excited-State Proton-Transfer in 2-Thiopyridone2019In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 25, no 7, p. 1733-1739Article in journal (Refereed)
    Abstract [en]

    Excited-state proton transfer (ESPT) is a fundamental process in biomolecular photochemistry, but its underlying mediators often evade direct observation. We identify a distinct pathway for ESPT in aqueous 2-thiopyridone, by employing transient N1s X-ray absorption spectroscopy and multi-configurational spectrum simulations. Photoexcitations to the singlet S-2 and S-4 states both relax promptly through intersystem crossing to the triplet T-1 state. The T-1 state, through its rapid population and near nanosecond lifetime, mediates nitrogen site deprotonation by ESPT in a secondary intersystem crossing to the S-0 potential energy surface. This conclusively establishes a dominant ESPT pathway for the system in aqueous solution, which is also compatible with previous measurements in acetonitrile. Thereby, the hitherto open questions of the pathway for ESPT in the compound, including its possible dependence on excitation wavelength and choice of solvent, are resolved.

  • 23. Eckert, Sebastian
    et al.
    Norell, Jesper
    Stockholm University, Faculty of Science, Department of Physics.
    Miedema, Piter S.
    Beye, Martin
    Fondell, Mattis
    Quevedo, Wilson
    Kennedy, Brian
    Hantschmann, Markus
    Pietzsch, Annette
    Van Kuiken, Benjamin E.
    Ross, Matthew
    Minitti, Michael P.
    Moeller, Stefan P.
    Schlotter, William F.
    Khalil, Munira
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Föhlisch, Alexander
    Ultrafast Independent N-H and N-C Bond Deformation Investigated with Resonant Inelastic X-Ray Scattering2017In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 56, no 22, p. 6088-6092Article in journal (Refereed)
    Abstract [en]

    The femtosecond excited-state dynamics following resonant photoexcitation enable the selective deformation of N-H and N-C chemical bonds in 2-thiopyridone in aqueous solution with optical or X-ray pulses. In combination with multiconfigurational quantum-chemical calculations, the orbital-specific electronic structure and its ultrafast dynamics accessed with resonant inelastic X-ray scattering at the N 1s level using synchrotron radiation and the soft X-ray free-electron laser LCLS provide direct evidence for this controlled photoinduced molecular deformation and its ultrashort time-scale.

  • 24. Eckert, Sebastian
    et al.
    Winghart, Marc-Oliver
    Kleine, Carlo
    Banerjee, Ambar
    Stockholm University, Faculty of Science, Department of Physics.
    Ekimova, Maria
    Ludwig, Jan
    Harich, Jessica
    Fondell, Mattis
    Mitzner, Rolf
    Pines, Ehud
    Huse, Nils
    Wernet, Philippe
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Nibbering, Erik T. J.
    Electronic Structure Changes of an Aromatic Amine Photoacid along the Förster Cycle2022In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 61, no 27, article id e202200709Article in journal (Refereed)
    Abstract [en]

    Photoacids show a strong increase in acidity in the first electronic excited state, enabling real-time studies of proton transfer in acid-base reactions, proton transport in energy storage devices and biomolecular sensor protein systems. Several explanations have been proposed for what determines photoacidity, ranging from variations in solvation free energy to changes in electronic structure occurring along the four stages of the Forster cycle. Here we use picosecond nitrogen K-edge spectroscopy to monitor the electronic structure changes of the proton donating group in a protonated aromatic amine photoacid in solution upon photoexcitation and subsequent proton transfer dynamics. Probing core-to-valence transitions locally at the amine functional group and with orbital specificity, we clearly reveal pronounced electronic structure, dipole moment and energetic changes on the conjugate photobase side. This result paves the way for a detailed electronic structural characterization of the photoacidity phenomenon.

  • 25. Ekholm, V.
    et al.
    Chiuzbǎian, G. S.
    Såthe, C.
    Nicolaou, A.
    Guarise, M.
    Simon, M.
    Jaouen, N.
    Lüning, J.
    Hague, C. F.
    Gel'mukhanov, F.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Björneholm, O.
    Rubensson, J.-E.
    Core-hole localization and ultra-fast dissociation in SF62020In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 53, no 18, article id 185101Article in journal (Refereed)
    Abstract [en]

    Resonant inelastic x-ray scattering spectra excited at the fluorine K resonances of SF(6)have been recorded. While a small but significant propensity for electronically parity-allowed transitions is found, the observation of parity-forbidden electronic transitions is attributed to vibronic coupling that breaks the global inversion symmetry of the electronic wavefunction and localizes the core hole. The dependence of the scattering cross section on the polarization of the incident radiation and the scattering angle is interpreted in terms of local pi/sigma symmetry around the S-F bond. This symmetry selectivity prevails during the dissociation that occurs during the scattering process.

  • 26. Ekimova, Maria
    et al.
    Kleine, Carlo
    Ludwig, Jan
    Ochmann, Miguel
    Agrenius, Thomas E. G.
    Kozari, Eve
    Pines, Dina
    Pines, Ehud
    Huse, Nils
    Wernet, Philippe
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Nibbering, Erik T. J.
    From Local Covalent Bonding to Extended Electric Field Interactions in Proton Hydration2022In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 61, no 46, article id e202211066Article in journal (Refereed)
    Abstract [en]

    Seemingly simple yet surprisingly difficult to probe, excess protons in water constitute complex quantum objects with strong interactions with the extended and dynamically changing hydrogen-bonding network of the liquid. Proton hydration plays pivotal roles in energy transport in hydrogen fuel cells and signal transduction in transmembrane proteins. While geometries and stoichiometry have been widely addressed in both experiment and theory, the electronic structure of these specific hydrated proton complexes has remained elusive. Here we show, layer by layer, how utilizing novel flatjet technology for accurate x-ray spectroscopic measurements and combining infrared spectral analysis and calculations, we find orbital-specific markers that distinguish two main electronic-structure effects: Local orbital interactions determine covalent bonding between the proton and neigbouring water molecules, while orbital-energy shifts measure the strength of the extended electric field of the proton. © 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.

  • 27. Ekimova, Maria
    et al.
    Kubin, Markus
    Ochmann, Miguel
    Ludwig, Jan
    Huse, Nils
    Wernet, Philippe
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Nibbering, Erik T. J.
    Soft X-ray Spectroscopy of the Amine Group: Hydrogen Bond Motifs in Alkylamine/Alkylammonium Acid-Base Pairs2018In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 122, no 31, p. 7737-7746Article in journal (Refereed)
    Abstract [en]

    We use N K-edge absorption spectroscopy to explore the electronic structure of the amine group, one of the most prototypical chemical functionalities playing a key role in acid base chemistry, electron donor-acceptor interactions, and nucleophilic substitution reactions. In this study, we focus on aliphatic amines and make use of the nitrogen is core electron excitations to elucidate the roles of N-H sigma* and N-C sigma* contributions in the unoccupied orbitals. We have measured N K-edge absorption spectra of the ethylamine bases EtxNH3-x (x = 0...3; Et- = C2H5-) and the conjugate positively charged ethylammonium cation acids EtyNH4-y+ (y = 0...4; Et- = C2H5-) dissolved in the protic solvents ethanol and water. Upon consecutive exchange of N-H for ethyl-groups, we observe a spectral shift, a systematic decrease of the N K-edge pre-edge peak, and a major contribution in the post edge region for the ethylamine series. Instead, for the ethylammonium ions, the consecutive exchange of N-H for ethyl groups leads to an apparent reduction of pre-edge and post-edge intensities relative to the main-edge band, without significant frequency shifts. Building on findings from our previously reported study on aqueous ammonia and ammonium ions, we can rationalize these observations by comparing calculated N K-edge absorption spectra of free and hydrogen-bonded clusters. Hydrogen bonding interactions lead only to minor spectral effects in the ethylamine series, but have a large impact in the ethylammonium ion series. Visualization of the unoccupied molecular orbitals shows the consecutive change in molecular orbital character from N-H sigma* to N-C sigma* in these alkylamine/alkylammonium ion series. This can act as a benchmark for future studies on chemically more involved amine compounds.

  • 28. Ekimova, Maria
    et al.
    Quevedo, Wilson
    Szyc, Łukasz
    Iannuzzi, Marcella
    Wernet, Philippe
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Nibbering, Erik T. J.
    Aqueous Solvation of Ammonia and Ammonium: Probing Hydrogen Bond Motifs with FT-IR and Soft X-ray Spectroscopy2017In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 139, no 36, p. 12773-12783Article in journal (Refereed)
    Abstract [en]

    In a multifaceted investigation combining local soft X-ray and vibrational spectroscopic probes with ab initio molecular dynamics simulations, hydrogen-bonding interactions of two key principal amine compounds in aqueous solution, ammonia (NH3) and ammonium ion (NH4+), are quantitatively assessed in terms of electronic structure, solvation structure, and dynamics. From the Xray measurements and complementary determination of the IR-active hydrogen stretching and bending modes of NH3 and NH4+ in aqueous solution, the picture emerges of a comparatively strongly hydrogen-bonded NH4+ ion via N-H donating interactions, whereas NH3 has a strongly accepting hydrogen bond with one water molecule at the nitrogen lone pair but only weakly N-H donating hydrogen bonds. In contrast to the case of hydrogen bonding among solvent water moleCules, we find that energy mismatch between occupied orbitals of both the solutes NH3 and NH4+ and the surrounding water prevents strong mixing between orbitals upon hydrogen bonding and, thus, inhibits substantial charge transfer between solute and solvent. A close inspection of the calculated unoccupied molecular orbitals, in conjunction with experimentally measured N K-edge absorption spectra, reveals the different nature of the electronic structural effects of these two key principal amine compounds imposed by hydrogen bonding to water, where a pH-dependent excitation energy appears to be an intrinsic property. These results provide a benchmark for hydrogen bonding of other nitrogen-containing acids and bases.

  • 29.
    Erbing, Axel
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Philippe, Bertrand
    Park, Byung-wook
    Cappel, Ute B.
    Rensmo, Håkan
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Spatial Microheterogeneity in the Valence Band in Mixed Halide Hybrid Perovskite MaterialsManuscript (preprint) (Other academic)
  • 30.
    Erbing, Axel
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Philippe, Bertrand
    Park, Byung-wook
    Cappel, Ute B.
    Rensmo, Håkan
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Spatial microheterogeneity in the valence band of mixed halide hybrid perovskite materials2022In: Chemical Science, ISSN 2041-6520, E-ISSN 2041-6539, Vol. 13, no 32, p. 9285-9294Article in journal (Refereed)
    Abstract [en]

    The valence band of lead halide hybrid perovskites with a mixed I/Br composition is investigated using electronic structure calculations and complementarily probed with hard X-ray photoelectron spectroscopy. In the latter, we used high photon energies giving element sensitivity to the heavy lead and halide ions and we observe distinct trends in the valence band as a function of the I : Br ratio. Through electronic structure calculations, we show that the spectral trends with overall composition can be understood in terms of variations in the local environment of neighboring halide ions. From the computational model supported by the experimental evidence, a picture of the microheterogeneity in the valence band maximum emerges. The microheterogeneity in the valence band suggests that additional charge transport mechanisms might be active in lead mixed halide hybrid perovskites, which could be described in terms of percolation pathways.

  • 31. Eriksson, Susanna K.
    et al.
    Hahlin, Maria
    Axnanda, Stephanus
    Crumlin, Ethan
    Wilks, Regan
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Eriksson, Anna I. K.
    Liu, Zhi
    Åhlund, John
    Hagfeldt, Anders
    Starr, David E.
    Bär, Marcus
    Rensmo, Håkan
    Siegbahn, Hans
    In-Situ Probing of H2O Effects on a Ru-Complex Adsorbed on TiO2 Using Ambient Pressure Photoelectron Spectroscopy2016In: Topics in catalysis, ISSN 1022-5528, E-ISSN 1572-9028, Vol. 59, no 5-7, p. 583-590Article in journal (Refereed)
    Abstract [en]

    Dye-sensitized interfaces in photocatalytic and solar cells systems are significantly affected by the choice of electrolyte solvent. In the present work, the interface between the hydrophobic Ru-complex Z907, a commonly used dye in molecular solar cells, and TiO2 was investigated with ambient pressure photoelectron spectroscopy (AP-PES) to study the effect of water atmosphere on the chemical and electronic structure of the dye/TiO2 interface. Both laboratory-based Al K alpha as well as synchrotron-based ambient pressure measurements using hard X-ray (AP-HAXPES) were used. AP-HAXPES data were collected at pressures of up to 25 mbar (i.e., the vapor pressure of water at room temperature) showing the presence of an adsorbed water overlayer on the sample surface. Adopting a quantitative AP-HAXPES analysis methodology indicates a stable stoichiometry in the presence of the water atmosphere. However, solvation effects due to the presence of water were observed both in the valence band region and for the S 1s core level and the results were compared with DFT calculations of the dye-water complex.

  • 32. Eriksson, Susanna K.
    et al.
    Josefsson, Ida
    Stockholm University, Faculty of Science, Department of Physics.
    Ellis, Hanna
    Amat, Anna
    Pastore, Mariachiara
    Oscarsson, Johan
    Lindblad, Rebecka
    Eriksson, Anna I. K.
    Johansson, Erik M. J.
    Boschloo, Gerrit
    Hagfeldt, Anders
    Fantacci, Simona
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Rensmo, Håkan
    Geometrical and energetical structural changes in organic dyes for dye-sensitized solar cells probed using photoelectron spectroscopy and DFT2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 1, p. 252-260Article in journal (Refereed)
    Abstract [en]

    The effects of alkoxy chain length in triarylamine based donor acceptor organic dyes are investigated with respect to the electronic and molecular surface structures on the performance of solar cells and the electron lifetime. The dyes were investigated when adsorbed on TiO2 in a configuration that can be used for dye sensitized solar cells (DSCs). Specifically, the two dyes D35 and D45 were compared using photoelectron spectroscopy (PES) and density functional theory (DFT) calculations. The differences in solar cell characteristics when longer alkoxy chains are introduced in the dye donor unit are attributed to geometrical changes in dye packing while only minor differences were observed in the electronic structure. A higher dye load was observed for D45 on TiO2. However, D35 based solar cells result in higher photocurrent although the dye load is lower. This is explained by different geometrical structures of the dyes on the surface.

  • 33. Eriksson, Susanna K.
    et al.
    Josefsson, Ida
    Stockholm University, Faculty of Science, Department of Physics.
    Ottosson, Niklas
    Öhrwall, Gunnar
    Björneholm, Olle
    Siegbahn, Hans
    Hagfeldt, Anders
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Rensmo, Hakan
    Solvent Dependence of the Electronic Structure of I- and I-3(-)2014In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 118, no 11, p. 3164-3174Article in journal (Refereed)
    Abstract [en]

    We present synchrotron-based I4d photoelectron spectroscopy experiments of solutions from LiI and LiI3 in water, ethanol, and acetonitrile. The experimentally determined solvent-induced binding energy shifts (SIBES) for the monatomic I- anion are compared to predictions from simple Born theory, PCM calculations, as well as multiconfigurational quantum chemical spectral calculations from geometries obtained through molecular dynamics of solvated clusters. We show that the SIBES for I- explicitly depend on the details of the hydrogen bonding configurations of the solvent to the I- and that static continuum models such as the Born model cannot capture the trends in the SIBES observed both in experiments and in higher-level calculations. To extend the discussion to more complex polyatomic anions, we also performed experiments on I-3(-) and I-/I-3(-) mixtures in different solvents and the results are analyzed in the perspective of SIBES. The experimental SIBES values indicate that the solvation effects even for such similar anions as I- and I-3(-) can be rather different in nature.

  • 34.
    Ertan, Emelie
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Kimberg, Victor
    Gel'mukhanov, Faris
    Hennies, Franz
    Rubensson, Jan-Erik
    Schmitt, Thorsten
    Strocov, Vladimir N.
    Zhou, Kejin
    Iannuzzi, Marcella
    Foehlisch, Alexander
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Pietzsch, Annette
    Theoretical simulations of oxygen K-edge resonant inelastic x-ray scattering of kaolinite2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 14, article id 144301Article in journal (Refereed)
    Abstract [en]

    Near-edge x-ray absorption fine structure (NEXAFS) and resonant inelastic x-ray scattering (RIXS) measurements at the oxygen K edge were combined with theoretical spectrum simulations, based on periodic density functional theory and nuclear quantum dynamics, to investigate the electronic structure and chemical bonding in kaolinite Al2Si2O5(OH)(4). We simulated NEXAFS spectra of all crystallographically inequivalent oxygen atoms in the crystal and RIXS spectra of the hydroxyl groups. Detailed insight into the ground-state potential energy surface of the electronic states involved in the RIXS process were accessed by analyzing the vibrational excitations, induced by the core excitation, in quasielastic scattering back to the electronic ground state. In particular, we find that the NEXAFS pre-edge is dominated by features related to OH groups within the silica and alumina sheets, and that the vibrational progression in RIXS can be used to selectively probe vibrational modes of this subclass of OH groups. The signal is dominated by the OH stretching mode, but also other lower vibrational degrees of freedom, mainly hindered rotational modes, contribute to the RIXS signal.

  • 35.
    Ertan, Emelie
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lundberg, Marcus
    Kragh Sørensen, Lasse
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Setting the stage for theoretical X-ray spectra of the H2S molecule with RASPT2 calculations of the energy landscapeManuscript (preprint) (Other academic)
    Abstract [en]

    Electronic valence- and core-excitations into the anti-bonding orbitals of the H2S molecule have been calculated within a multi-configurational wave-function framework (RASPT2). Potential energy surfaces and transition dipole moments have been derived in two dimensions for the S-H stretching coordinates. The |S1s-1, 6a11> and |S1s-1, 3b21> core-excited states in H2S are nearly degenerate along the symmetric stretching coordinate, for which we have identified two conical intersections. The small energy splitting of the S1s-1 core-excited states at equilibrium geometry arise from an avoided crossing at broken symmetry. Compared to the water molecule, which exhibit state-selective gating to different vibrational modes [Nat. Commun. 8 14165 (2017)] in its well-separated O1s-1 core-excited states, we expect a strong coupling between the close-lying |S1s-1, 6a11> and |S1s-1, 3b21> states. This could lead to dissociative dynamics observable in K-edge RIXS. The S2p-1 core-excited states form two dense manifolds of spin-orbit coupled states, which can be schematically characterised as bound |S2p-1,3b21> and dissociative |S2p-1,6a11> states. We identify three conical intersections in the singlet and triplet states along the symmetric stretching coordinate. Mapping the molecular singlet and triplet states to the atomic dissociation limit reveals a symmetry selection rule, leading to an off-set of the 1|3a1-1,6a11> state relative to the other S2p-1 core-excited states. The dense manifolds of S2p-1 core-excited states will complicate the analysis of Kα-edge RIXS, but dynamical effects could be evaluated through detuning and in comparison to L-edge XAS. In L-edge RIXS, the dynamical effects well be more pronounced due to a longer life-time of the S2p-1 core-excited states compared to the S1s-1 core-excited states.

  • 36.
    Ertan, Emelie
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lundberg, Marcus
    Sørensen, Lasse Kragh
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Setting the stage for theoretical x-ray spectra of the H2S molecule with multi-configurational quantum chemical calculations of the energy landscape2020In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 152, no 9, article id 094305Article in journal (Refereed)
    Abstract [en]

    In the H2S molecule, the interplay between different core levels can be investigated in great detail in relation to x-ray spectroscopy, which requires a theory for interpretation. Hence, valence and core excitations into the two antibonding molecular orbitals of the H2S molecule have been calculated within a multi-configurational wave function framework. Scanning along the S-H stretching coordinates, we derive potential energy surfaces and transition dipole moments involving the ground state and core and valence excited states. Both valence excitations and the S1s(-1) and S2p(-1) core excitations show pairs of dissociative and bound electronic states. These pairs of states are nearly degenerate in H2S at the ground state geometry. The close degeneracy together with conical intersections makes H2S an interesting target for x-ray spectroscopy involving ultra-fast dissociation influenced by non-adiabatic transitions and interference. For future investigations with x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS), it is valuable to compare H2S with the water molecule, which exhibits state-selective gating to different vibrational modes [R. C. Couto et al., Nat. Commun. 8, 14165 (2017)] in its well-separated O1s(-1) core excited states. The dense manifolds of the S2p(-1) core excited states will complicate the analysis of K-alpha edge RIXS, but dynamical effects could be evaluated through detuning and by comparing with L edge XAS. In L edge RIXS, the dynamical effects will be more pronounced due to the longer lifetime of the S2p(-1) core excited states compared to the S1s(-1) core excited states.

  • 37.
    Ertan, Emelie
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Savchenko, Viktoriia
    Ignatova, Nina
    da Cruz, Vinicius Vaz
    Couto, Rafael C.
    Eckert, Sebastian
    Fondell, Mattis
    Dantz, Marcus
    Kennedy, Brian
    Schmitt, Thorsten
    Pietzsch, Annette
    Foelisch, Alexander
    Gel'mukhanov, Faris
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Kimberg, Victor
    Ultrafast dissociation features in RIXS spectra of the water molecule2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 21, p. 14384-14397Article in journal (Refereed)
    Abstract [en]

    In this combined theoretical and experimental study we report on an analysis of the resonant inelastic X-ray scattering (RIXS) spectra of gas phase water via the lowest dissociative core-excited state |1s-1O4a11. We focus on the spectral feature near the dissociation limit of the electronic ground state. We show that the narrow atomic-like peak consists of the overlapping contribution from the RIXS channels back to the ground state and to the first valence excited state |1b-114a11 of the molecule. The spectral feature has signatures of ultrafast dissociation (UFD) in the core-excited state, as we show by means of ab initio calculations and time-dependent nuclear wave packet simulations. We show that the electronically elastic RIXS channel gives substantial contribution to the atomic-like resonance due to the strong bond length dependence of the magnitude and orientation of the transition dipole moment. By studying the RIXS for an excitation energy scan over the core-excited state resonance, we can understand and single out the molecular and atomic-like contributions in the decay to the lowest valence-excited state. Our study is complemented by a theoretical discussion of RIXS in the case of isotopically substituted water (HDO and D2O) where the nuclear dynamics is significantly affected by the heavier fragments' mass.

  • 38.
    Ertan, Emelie
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Savchenko, Viktoriia
    Ignatova, Nina
    Vaz da Cruz, Vinicius
    Couto, Rafael
    Eckert, Sebastian
    Fondell, Mattis
    Dantz, Marcus
    Kennedy, Brian
    Schmitt, Thorsten
    Pietzsch, Annette
    Föhlisch, Alexander
    Gel'mukhanov, Faris
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Kimberg, Victor
    Ultrafast dissociation features in RIXS spectra of the water moleculeManuscript (preprint) (Other academic)
    Abstract [en]

    In this combined theoretical and experimental study we report on an analysis of the resonant inelastic X-ray scattering spectra (RIXS) of gas phase water via the lowest dissociative core-excited state |1sO-14a11>. We focus on the spectral feature near the dissociation limit of the electronic ground state. We show that the narrow atomic-like peak consists of the overlapping contribution from the RIXS channels  back to the ground state and to the first valence excited state |1b1-14a11> of the molecule. The spectral feature has signatures of ultrafast dissociation (UFD) in the core-excited state, as we show by means of ab initio calculations and time-dependent nuclear wave packet simulations. We show that the electronically elastic RIXS channel gives substantial contribution to the atomic-like resonance due to the strong bond length dependence of the magnitude and orientation of the transition dipole moment. By studying the RIXS for an excitation energy scan over the core-excited state resonance, we can understand and single out the molecular and atomic-like contributions in the decay to the lowest valence-excited state. Our study is complemented by a theoretical discussion of RIXS in the case of the isotope substituted water (HDO and D2O) where the nuclear dynamics is significantly affected by the heavier fragments' mass.

  • 39. Gadegaard, Ane Riis
    et al.
    Thogersen, Jan
    Jensen, Svend Knak
    Nielsen, Jakob Brun
    Jena, Naresh K.
    Stockholm University, Faculty of Science, Department of Physics.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Jensen, Frank
    Keiding, Søren Rud
    Spectroscopy and picosecond dynamics of aqueous NO22014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 141, no 6, p. 064310-Article in journal (Refereed)
    Abstract [en]

    We investigate the formation of aqueous nitrogen dioxide, NO2 formed through femtosecond photolysis of nitrate, NO3- ( aq) and nitromethane CH3NO2(aq). Common to the experiments is the observation of a strong induced absorption at 1610 +/- 10 cm(-1), assigned to the asymmetric stretch vibration in the ground state of NO2. This assignment is substantiated through isotope experiments substituting N-14 by N-15, experiments at different pH values, and by theoretical calculations and simulations of NO2-D2O clusters.

  • 40. Gaffney, K. J.
    et al.
    Ji, M.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Park, S.
    Sun, Z.
    H-bond switching and ligand exchange dynamics in aqueous ionic solution2011In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 504, no 1-3, p. 1-6Article in journal (Refereed)
    Abstract [en]

    Aqueous ionic solutions lubricate the chemical machinery of the environment and life. Understanding the impact of ions on the properties of aqueous solutions and how these modified properties influence chemical and conformational dynamics remains an important and elusive objective of physical chemistry research. Here we discuss recent advances in our understanding that have been derived from ultrafast vibrational spectroscopy and molecular dynamics simulations.

  • 41. García-Fernández, Alberto
    et al.
    Svanström, Sebastian
    Sterling, Cody M.
    Stockholm University, Faculty of Science, Department of Physics.
    Gangan, Abhijeet
    Stockholm University, Faculty of Science, Department of Physics.
    Erbing, Axel
    Stockholm University, Faculty of Science, Department of Physics.
    Kamal, Chinnathambi
    Stockholm University, Faculty of Science, Department of Physics. Raja Ramanna Centre for Advanced Technology, India; Homi Bhabha National Institute, India.
    Sloboda, Tamara
    Kammlander, Birgit
    Man, Gabriel J.
    Rensmo, Håkan
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Cappel, Ute B.
    Experimental and Theoretical Core Level and Valence Band Analysis of Clean Perovskite Single Crystal Surfaces2022In: Small, ISSN 1613-6810, E-ISSN 1613-6829, Vol. 18, no 13, article id 2106450Article in journal (Refereed)
    Abstract [en]

    A detailed understanding of the surface and interface properties of lead halide perovskites is of interest for several applications, in which these materials may be used. To develop this understanding, the study of clean crystalline surfaces can be an important stepping stone. In this work, the surface properties and electronic structure of two different perovskite single crystal compositions (MAPbI3 and CsxFA1–xPbI3) are investigated using synchrotron-based soft X-ray photoelectron spectroscopy (PES), molecular dynamics simulations, and density functional theory. The use of synchrotron-based soft X-ray PES enables high surface sensitivity and nondestructive depth-profiling. Core level and valence band spectra of the single crystals are presented. The authors find two carbon 1s contributions at the surface of MAPbI3 and assign these to MA+ ions in an MAI-terminated surface and to MA+ ions below the surface. It is estimated that the surface is predominantly MAI-terminated but up to 30% of the surface can be PbI2-terminated. The results presented here can serve as reference spectra for photoelectron spectroscopy investigations of technologically relevant polycrystalline thin films, and the findings can be utilized to further optimize the design of device interfaces.

  • 42. Gel'mukhanov, Faris
    et al.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Polyutov, Sergey P.
    Föhlisch, Alexander
    Kimberg, Victor
    Dynamics of resonant x-ray and Auger scattering2021In: Reviews of Modern Physics, ISSN 0034-6861, E-ISSN 1539-0756, Vol. 93, no 3, article id 035001Article, review/survey (Refereed)
    Abstract [en]

    An overview of both experimental and theoretical results in the field of resonant scattering of tunable soft and hard x-ray radiation is presented, with a main focus on the closely related processes of resonant inelastic x-ray scattering (RIXS) and resonant Auger scattering (RAS). The review starts with an overview of fundamental dynamical aspects of RIXS illustrated for different systems. A detailed analysis of case studies with increasing complexity, considering both gas-phase and condensed matter (liquids and solids) applications, is given. In the review, the most important achievements in investigations of coupled electron-nuclear dynamics and structural aspects in studies of liquids and solids over the last two decades are outlined. To give a perspective on the insights from RIXS and RAS, the x-ray results are discussed against the background of complementary experimental techniques like vibrational infrared absorption and Raman spectroscopy, as well as small-angle x-ray and neutron scattering. Finally, recent achievements in time-resolved studies based on x-ray free-electron lasers are described.

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  • 43. Grönbeck, Henrik
    et al.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Photoemission core-level shifts reveal the thiolate-Au(111) interface2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, p. 085416-Article in journal (Refereed)
    Abstract [en]

    The nature of the thiolate/Au(111) interface is a long-standing puzzle. It has been suggested that thiolates drive surface reconstruction, however, a consensus regarding the adsorption configuration is missing. Herein, the density-functional theory is used to evaluate surface core-level shifts (SCLSs) for methyl thiolates on Au(111) assuming a representative set of different surface reconstructions. The SCLSs are found to provide sensitive fingerprints of the anchoring configuration, and it is only thiolate adsorption in the form of MeS-Au-SMe complexes that can be reconciled with experimental data.

  • 44.
    Hahlin, Maria
    et al.
    Uppsala universitet.
    Johansson, Erik M J
    Uppsala universitet.
    Plogmaker, Stefan
    Uppsala universitet.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Hagberg, Daniel P
    Sun, Licheng
    KTH, Organisk kemi.
    Siegbahn, Hans
    Uppsala universitet.
    Rensmo, Håkan
    Uppsala universitet.
    Electronic and molecular structures of organic dye/TiO(2) interfaces for solar cell applications: a core level photoelectron spectroscopy study.2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 7, p. 1507-17Article in journal (Refereed)
    Abstract [en]

    The electronic and molecular properties of three organic dye molecules with the general structure donor-linker-anchor have been investigated using core level photoelectron spectroscopy (PES). The molecules contain a diphenylaniline donor unit, a thiophene linker unit, and cyanoacrylic acid or rhodanine-3-acetic acid anchor units. They have been investigated both in the form of a multilayer and adsorbed onto nanoporous TiO(2) and the experimental results were also compared with DFT calculations. The changes at the dye-sensitized TiO(2) surface due to the modification of either the donor unit or the anchor unit was investigated and the results showed important differences in coverage as well as in electronic and molecular surface properties. By measuring the core level binding energies, the sub-molecular properties were characterized and the result showed that the adsorption to the TiO(2) influences the energy levels of the sub-molecular units differently.

  • 45. Hahlin, Maria
    et al.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Magnuson, Martin
    Johansson, Erik M. J.
    Plogmaker, Stefan
    Hagberg, Daniel P.
    Sun, Licheng
    Siegbahn, Hans
    Rensmo, Håkan
    Mapping the frontier electronic structures of triphenylamine based organic dyes at TiO2 Interafaces2011In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, p. 3534--3546Article in journal (Refereed)
    Abstract [en]

    The frontier electronic structures of a series of organic dye molecules containing a triphenylamine moiety, a thiophene moiety and a cyanoacrylic acid moiety have been investigated by photoelectron spectroscopy (PES), X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and resonant photoelectron spectroscopy (RPES). The experimental results were compared to electronic structure calculations on the molecules, which are used to confirm and enrich the assignment of the spectra. The approach allows us to experimentally measure and interpret the basic valence energy level structure in the dye, including the highest occupied energy level and how it depends on the interaction between the different units. Based on N 1s X-ray absorption and emission spectra we also obtain insight into the structure of the excited states, the molecular orbital composition and dynamics. Together the results provide an experimentally determined energy level map useful in the design of these types of materials. Included are also results indicating femtosecond charge redistribution at the dye/TiO2 interface.

  • 46.
    Hedvall, Patrik
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Charge transfer in sodium iodide collisions2023In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 158, no 1, article id 014305Article in journal (Refereed)
    Abstract [en]

    Sodium iodide (NaI) has, over the years, served as a prototype system in studies of non-adiabatic dynamics. Here, the charge transfer collision reactions Na+ + I− ⇆ Na + I (mutual neutralization and ion-pair formation) are studied using an ab initio approach and the total and differential cross sections are calculated for the reactions. This involves electronic structure calculations on NaI to obtain adiabatic potential energy curves, non-adiabatic and spin–orbit couplings, followed by nuclear dynamics, treated fully quantum mechanically in a strictly diabatic representation. A single avoided crossing at 13.22 a0 dominates the reactions, and the total cross sections are well captured by the semi-classical Landau–Zener model. Compared to the measured ion-pair formation cross section, the calculated cross section is about a factor of two smaller, and the overall shape of the calculated differential cross section is in reasonable agreement with the measured ion-pair formation differential cross section. Treating the Landau–Zener coupling as an empirical parameter of 0.05 eV, the measured total and differential cross sections are well captured when performing fully quantum mechanical cross section calculations including rotational coupling. A semi-empirical spin–orbit coupling model is also investigated, giving satisfactory estimation of the effects of spin–orbit interactions for the reactions. 

  • 47. Ignatova, Nina
    et al.
    Cruz, Vinicius V.
    Couto, Rafael C.
    Ertan, Emelie
    Stockholm University, Faculty of Science, Department of Physics.
    Zimin, Andrey
    Guimaraes, Freddy F.
    Polyutov, Sergey
    Ågren, Hans
    Kimberg, Victor
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Gel'mukhanov, Faris
    Gradual collapse of nuclear wave functions regulated by frequency tuned X-ray scattering2017In: Scientific Reports, E-ISSN 2045-2322, Vol. 7, article id 43891Article in journal (Refereed)
    Abstract [en]

    As is well established, the symmetry breaking by isotope substitution in the water molecule results in localisation of the vibrations along one of the two bonds in the ground state. In this study we find that this localisation may be broken in excited electronic states. Contrary to the ground state, the stretching vibrations of HDO are delocalised in the bound vertical bar 1a(1)(-1) 2b(2)(>)(1) core-excited state in spite of the mass difference between hydrogen and deuterium. The reason for this effect can be traced to the narrow canyon-like shape of the potential of the vertical bar 1a(1)(-1) 2b(2)(1 >) state along the symmetric stretching mode, which dominates over the localisation mass-difference effect. In contrast, the localisation of nuclear motion to one of the HDO bonds is preserved in the dissociative core-excited state vertical bar 1a(1)(-1) 4a(1)(1 >) . The dynamics of the delocalisation of nuclear motion in these core- excited states is studied using resonant inelastic X-ray scattering of the vibrationally excited HDO molecule. The results shed light on the process of a wave function collapse. After core-excitation into the vertical bar 1a(1)(-1) 2b(2)(1 >) state of HDO the initial wave packet collapses gradually, rather than instantaneously, to a single vibrational eigenstate.

  • 48. Ignatova, Nina
    et al.
    da Cruz, Vinicius V.
    Couto, Rafael C.
    Ertan, Emilie
    Stockholm University, Faculty of Science, Department of Physics.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Ågren, Hans
    Guimaraes, Freddy F.
    Zimin, Andrei
    Polyutov, Sergey P.
    Gel'mukhanov, Faris
    Kimberg, Victor
    Infrared-pump-x-ray-probe spectroscopy of vibrationally excited molecules2017In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 95, no 4, article id 042502Article in journal (Refereed)
    Abstract [en]

    We develop a theory of infrared (IR)-pump-x-ray-probe spectroscopy for molecular studies. We illustrate advantages of the proposed scheme by means of numerical simulations employing a vibrational wave packet technique applied to x-ray absorption and resonant inelastic x-ray scattering (RIXS) spectra of the water molecule vibrationally excited by a preceding IR field. The promotion of the vibrationally excited molecule to the dissociative 1a(1)(-1)4a(1) and bound 1a(1)(-1)2b(2) core-excited states with qualitatively different shapes of the potential energy surfaces creates nuclear wave packets localized along and between the OH bonds, respectively. The projection of these wave packets on the final vibrational states, governed by selection and propensity rules, results in spatial selectivity of RIXS sensitive to the initial vibrationally excited state, which makes it possible to probe selectively the ground state properties along different modes. In addition, we propose to use RIXS as a tool to study x-ray absorption from a selected vibrational level of the ground state when the spectral resolution is sufficiently high to resolve vibrational overtones. The proposed technique has potential applications for advanced mapping of multidimensional potential energy surfaces of ground and core-excited molecular states, for symmetry-resolved spectroscopy, and for steering chemical reactions.

  • 49. Ingle, R. A.
    et al.
    Banerjee, Ambar
    Stockholm University, Faculty of Science, Department of Physics.
    Bacellar, C.
    Barillot, T. R.
    Longetti, L.
    Coreno, M.
    de Simone, M.
    Zuccaro, F.
    Poletto, L.
    Miotti, P.
    Röder, A.
    Stolow, A.
    Schuurman, M. S.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Chergui, M.
    Carbon K-edge x-ray emission spectroscopy of gas phase ethylenic molecules2022In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 55, no 4, article id 044001Article in journal (Refereed)
    Abstract [en]

    We report on the C K-edge x-ray absorption spectra and the resonant (RXES) and non-resonant (NXES) x-ray emission spectra of ethylene, allene and butadiene in the gas phase. The RXES and NXES show clear differences for the different molecules. Overall both types of spectra are more structured for ethylene and allene, than for butadiene. Using density functional theory–restricted open shell configuration interaction single calculations, we simulate the spectra with remarkable agreement with the experiment. We identify the spectral features as being due to transitions involving localised 1s orbitals. For allene, there are distinct spectral bands that reflect transitions predominantly from either the central or terminal carbon atoms. These results are discussed in the context of ultrafast x-ray studies aimed at detecting the passage through conical intersections in polyatomic molecules.

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  • 50. Jain, Kalpna
    et al.
    Kaniyankandy, Sreejith
    Kishor, Shyam
    Josefsson, Ida
    Stockholm University, Faculty of Science, Department of Physics.
    Ghosh, Hirendra N.
    Singh, Khundrakpam S.
    Mookerjee, Sumit
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Ramaniah, Lavanya M.
    Density functional investigation and some optical experiments on dye-sensitized quantum dots2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 43, p. 28683-28696Article in journal (Refereed)
    Abstract [en]

    Dye-sensitized quantum dots (QDs) are promising candidates for dye-sensitized solar cells (DSSCs). Here, we report steady state (absorption and photoluminescence) optical measurements on several sizes of CdS QDs ligated with Coumarin 343 dye (C-343) and two different solvents, viz., chloroform and toluene. We further report detailed first principles density functional theory and time-dependent density functional theory studies of the geometric, electronic and optical (absorption and emission) properties of three different sized capped QDs, ligated with C-343 dye. The absorption spectrum shows a QD-size-independent peak, and another peak which shifts to blue with decrease in QD size. The first peak is found to arise from the dye molecule and the second one from the QD. Charge transfer using natural transition orbitals (NTOs) is found to occur from dye-to-QDs and is solvent-dependent. In the emission spectra, the luminescence intensity of the dye is quenched by the addition of the QD indicating a strong interaction between the QD and the dye.

123 1 - 50 of 139
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