Markus Kowalewski

Markus Kowalewski

Biträdande lektor

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Arbetar vid Fysikum
Telefon 08-553 786 61
Besöksadress Roslagstullsbacken 21
Rum C4:3041
Postadress Fysikum 106 91 Stockholm

Om mig

The group works on a wide variety of topics involving photo chemistry, coherent control, polaritonic chemistry, ultrafast spectroscopy, and numerical methods related to quantum dynamics.

Polaritonic Chemistry and Light-Matter Materials

Gaining detailed control over chemical reactions has always been a chemists dream. Quantum coherent control has been pursuing this dream by using specially tailored light fields to control chemical reactions on an atomistic level. With the advancement of cavity quantum electrodynamics and its recent application to molecules, using the quantum properties of light to control photo-chemistry has come into reach. Recent,
ground breaking experiments have show that one can utilize the vacuum field of an optical nano-resonator to significantly modify the potential energy landscape and thus its photo-chemistry. The underlying effect is the formation of so called "dressed states", which are created when the quantized radiation field mode couples to a molecular electronic transition. In the resulting coupled light-matter system the molecular and the photonic degrees of freedom are heavily mixed. While this effect is well understood for atomic samples, it is not yet fully understood for molecules. The introduction of the nuclear degrees of freedom requires new theoretical frameworks. This effect can be used to modify reaction pathways of chemical and photo-chemical reactions. This opens a wide range of possibilities to engineer novel types of light driven catalysts. We are looking at the underlying mechanisms and are working on building a suitable tool chest for numerical simulations. With the new insight and tools we want to propose new photo-chemical applications.

Ultrafast X-Ray Spectroscopy of Conical Intersections

Conical intersections (CoIns) so far have eluded direct experimental observations. The evidence for their existence is based on ultra fast relaxation rates and other indirect signatures. The rapidly varying energy gap in the vicinity of a C oIn poses a main obstacle for their direct detection. The required extreme combination of temporal and spectral resolution is not available in conventional optical femtosecond experiments. Ultra short laser pulses in the extreme ultraviolet and X-ray laser regime, as they are provided by free electron laser and high harmonic generation sources, fulfill the spectral and temporal requirements to resolve the coupled nuclear+electronic dynamics in the vicinity of CoIns. Ultrafast hard X-ray sources make time-resolved diffraction experiments possible, paving the way to capture the nuclear dynamics of molecules in time as well as in space, with the "molecular movie" of a CoIn as the ultimate goal.

We theoretically investigate novel, X-Ray baseed experimental techniques for spectroscopic detection of CoIns with ultra short X-ray pulses. Simulation strategies for non-linear X-ray spectra and diffraction schemes are applied to molecular system of increasing complexity.


I urval från Stockholms universitets publikationsdatabas
  • 2019. Daeheum Cho (et al.). Philosophical Transactions. Series A 377 (2145)

    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.

  • 2019. Markus Kowalewski, Kochise Bennett, Shaul Mukamel. EPJ Web of Conferences 205

    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.

  • 2018. Riccardo Mincigrucci (et al.). Scientific Reports 8

    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.

  • 2018. Kochise Bennett (et al.). Proceedings of the National Academy of Sciences of the United States of America 115 (26), 6538-6547

    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.

  • 2018. Vladimir Al. Osipov, Markus Kowalewski, Shaul Mukamel. Proceedings of the National Academy of Sciences of the United States of America 115 (41), 10269-10274

    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.

Visa alla publikationer av Markus Kowalewski vid Stockholms universitet

Senast uppdaterad: 21 september 2019

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