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  • 1. Bennett, Kochise
    et al.
    Kowalewski, Markus
    University of California, USA.
    Rouxel, Jeremy R.
    Mukamel, Shaul
    Monitoring molecular nonadiabatic dynamics with femtosecond X-ray diffraction2018In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 115, no 26, p. 6538-6547Article in journal (Refereed)
    Abstract [en]

    Ultrafast time-resolved X-ray scattering, made possible by free-electron laser sources, provides a wealth of information about electronic and nuclear dynamical processes in molecules. The technique provides stroboscopic snapshots of the time-dependent electronic charge density traditionally used in structure determination and reflects the interplay of elastic and inelastic processes, nonadiabatic dynamics, and electronic populations and coherences. The various contributions to ultrafast off-resonant diffraction from populations and coherences of molecules in crystals, in the gas phase, or from single molecules are surveyed for core-resonant and off-resonant diffraction. Single-molecule proportional to N scaling and two-molecule proportional to N-2 scaling contributions, where N is the number of active molecules, are compared. Simulations are presented for the excited-state nonadiabatic dynamics of the electron harpooning at the avoided crossing in NaF. We show how a class of multiple diffraction signals from a single molecule can reveal charge-density fluctuations through multidimensional correlation functions of the charge density.

  • 2. Cho, Daeheum
    et al.
    Rouxel, Jérémy R.
    Kowalewski, Markus
    Stockholm University, Faculty of Science, Department of Physics.
    Lee, Jin Yong
    Mukamel, Shaul
    Imaging of transition charge densities involving carbon core excitations by all X-ray sum-frequency generation2019In: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 377, no 2145, article id 2017.0470Article in journal (Refereed)
    Abstract [en]

    X-ray diffraction signals from the time-evolving molecular charge density induced by selective core excitation of chemically inequivalent carbon atoms are calculated. A narrowband X-ray pulse selectively excites the carbon K-edge of the –CH3 or –CH2F groups in fluoroethane (CH3–CH2F). Each excitation creates a distinct core coherence which depends on the character of the electronic transition. Direct propagation of the reduced single-electron density matrix, using real-time time-dependent density functional theory, provides the time-evolving charge density following interactions with external fields. The interplay between partially filled valence molecular orbitals upon core excitation induces characteristic femtosecond charge migration which depends on the core–valence coherence, and is monitored by the sum-frequency generation diffraction signal.

  • 3. Csehi, András
    et al.
    Kowalewski, Markus
    Stockholm University, Faculty of Science, Department of Physics.
    Halász, Gábor J.
    Vibók, Ágnes
    Ultrafast dynamics in the vicinity of quantum light-induced conical intersections2019In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 21, article id 093040Article in journal (Refereed)
    Abstract [en]

    Nonadiabatic effects appear due to avoided crossings or conical intersections (CIs) that are either intrinsic properties in field-free space or induced by a classical laser field in a molecule. It was demonstrated that avoided crossings in diatomics can also be created in an optical cavity. Here, the quantized radiation field mixes the nuclear and electronic degrees of freedom creating hybrid field-matter states called polaritons. In the present theoretical study we go further and create CIs in diatomics by means of a radiation field in the framework of cavity quantum electrodynamics. By treating all degrees of freedom, that is the rotational, vibrational, electronic and photonic degrees of freedom on an equal footing we can control the nonadiabatic quantum light-induced dynamics by means of CIs. First, the pronounced difference between the the quantum light-induced avoided crossing and the CI with respect to the nonadiabatic dynamics of the molecule is demonstrated. Second, we discuss the similarities and differences between the classical and the quantum field description of the light for the studied scenario.

  • 4.
    Kowalewski, Markus
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Bennett, Kochise
    Mukamel, Shaul
    Monitoring nonadiabatic dynamics in molecules by ultrafast X-Ray diffraction2019In: EPJ Web of Conferences, ISSN 2101-6275, E-ISSN 2100-014X, Vol. 205, article id 09032Article in journal (Refereed)
    Abstract [en]

    We theoretically examine time-resolved diffraction from molecules which undergo non-adiabatic dynamics and identify contributions from inelastic scattering that indicate the presence of an avoided crossing and the corresponding nuclear configuration.

  • 5. Mincigrucci, Riccardo
    et al.
    Kowalewski, Markus
    University of California, USA.
    Rouxel, Jérémy R.
    Bencivenga, Filippo
    Mukamel, Shaul
    Masciovecchio, Claudio
    Impulsive UV-pump/X-ray probe study of vibrational dynamics in glycine2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 15466Article in journal (Refereed)
    Abstract [en]

    We report an ab-initio study of a pump-probe experiment on the amino-acid glycine. We consider an UV pump followed by an X-ray probe tuned to carbon K-edge and study the vibronic structure of the core transition. The simulated experiment is feasible using existing free electron laser or high harmonic generation sources and thanks to the localization of the core orbitals posseses chemical selectivity. The present theory applies to other experimental schemes, including the use of a THz probe, available with present soft X-ray free electron lasers and/or high harmonic generation sources.

  • 6. Osipov, Vladimir Al.
    et al.
    Kowalewski, Markus
    Stockholm University, Faculty of Science, Department of Physics.
    Mukamel, Shaul
    Multiscale wavelet decomposition of time-resolved X-ray diffraction signals in cyclohexadiene2018In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 115, no 41, p. 10269-10274Article in journal (Refereed)
    Abstract [en]

    We demonstrate how the wavelet transform, which is a powerful tool for compression, filtering, and scaling analysis of signals, may be used to separate large- and short-scale electron density features in X-ray diffraction patterns. Wavelets can isolate the electron density associated with delocalized bonds from the much stronger background of highly localized core electrons. The wavelet-processed signals clearly reveal the bond formation and breaking in the early steps of the photoinduced pericyclic ring opening reaction of 1,3-cyclohexadiene, which are not resolved in the bare signal.

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