Tuesday 5 pm (Freiburg) / 8 am (Vancouver)

18.10.2022 – Jennifer Meyer, TU Kaiserslautern

25.10.2022 – cancelled

08.11.2022 – Patrick Rupprecht, MPI für Kernphysik Heidelberg

15.11.2022 – Volker Karle, ISTA Austria

22.11.2022 – Graziano Amati, University of Freiburg

29.11.2022 – Francisco Gonzalez Montoya, University of Leeds, UK

06.12.2022 – Albert Stolow, University Ottawa, Canada

13.12.2022 – Donatas Zigmantas, Lund University, Sweden

20.12.2022 – Oriol Vendrell, University of Heidelberg

10.01.2023 – Abolfazl Bayat, Chengdu University, China

17.01.2023 – Nina Morgner, University of Frankfurt

24.01.2023 – Serguei Patchovski, MBI Berlin

31.01.2023 – Sara Bonella, EPFL Lausanne, Switzerland

07.02.2023 – Zdenek Masin, Charles University Prague, Czechia

29.11.2022 – Francisco Gonzalez Montoya, University of Leeds, UK

The calculation of long term dynamics of a spin chain using coherent states

The time dependent variational principle and  the coherent states has been successfully used to calculate the evolution of quantum systems with classical analog. Based on this approach, we explore the possibility to calculate the long term dynamics of an experimental time dependent spin chain.

Chair: Andreas Buchleitner

22.11.2022 – Graziano Amati, University of Freiburg

Quasiclassical approaches to nonadiabatic dynamics

In this talk I will discuss quasiclassical techniques aimed at accurately predicting quantum nonadiabatic dynamics at long time with a favorable classical scaling with time and system size. In particular, I will introduce spin mapping, a recently developed quasiclassical approach suited to study a large class of nonadiabatic systems out-of-equilibrium. Spin mapping, although substantially more accurate than Ehrenfest mean-field dynamics, can suffer from low accuracy in the long-time dynamics of strongly asymmetric systems. I will show how such limitation can be overcome by coupling the method to the formalism of the generalized quantum master equation. On the other side, the same strategy applied to Ehrenfest dynamics does not result in meaningful improvements in accuracy. In the second part of the talk I will introduce ellipsoid mapping, a method that we recently developed by generalizing spin mapping to study nonadiabatic systems in thermal equilibrium. The approach fulfills detailed balance by construction; in particular, the method is time reversible, and it guarantees the correct long-time relaxation of thermal correlation functions.

References:

 – G. Amati, M. A. C. Saller, A. Kelly, J. O. Richardson,

https://arxiv.org/abs/2209.01076 (2022)

 – J. E. Runeson, J. R. Mannouch, G. Amati, M. R. Fiechter, J. O.

Richardson, Chimia 76 582–588 (2022)

Chair: Tanja Schilling

15.11.2022 – Volker Karle, Institute of Science and Technology Austria

Multiband topological phases of periodically kicked molecules

In this talk will show that the simplest of existing molecules – closed-shell diatomics not interacting with one another – host topologically nontrivial phases when driven by periodic far-off-resonant laser pulses. A periodically kicked molecular rotor can be mapped onto a “crystalline“ lattice in angular momentum space. This allows to define quasimomenta and the band structure in the Floquet representation, by analogy with the Bloch waves of solid-state physics. Applying laser pulses spaced by 1/3 of the molecular rotational period creates a lattice with three atoms per unit cell with staggered hopping, whose band structure features Dirac cones. These Dirac cones, topologically protected by reflection and time-reversal symmetry, are reminiscent of (although not equivalent to) the ones seen in graphene. They – and the corresponding edge states – are broadly tunable by adjusting the laser intensities and can be observed in present-day experiments by measuring molecular alignment and populations of rotational levels. This paves the way to study controllable topological physics in gas-phase experiments with small molecules as well as to classify dynamical molecular states by their topological invariants.

Chair: Andreas Buchleitner

08.11.2022 – Patrick Rupprecht, MPI für Kernphysik Heidelberg

From femtoseconds to femtometers – controlling quantum dynamics in molecules using core-level transient absorption spectroscopy

Core-level absorption spectroscopy has proven to be a valuable tool to gain a deeper understanding of quantum dynamics in atoms, molecules and solid-state materials on the femtosecond time scale. Especially the capability of x-ray transient absorption spectroscopy (XTAS) to elucidate dynamics in neutral and thus chemically highly relevant molecules stands out.
In this talk I will present a novel few-cycle laser source and transient absorption setup at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. In addition, first results of purely electronic as well as structural control within molecules using intense femtosecond laser pulses are discussed.
The performed XTAS experiments are enabled by a laser source providing center-wavelength tunable few-cycle pulses in the 1-2 µm short-wavelength infrared (SWIR) regime. These pulses drive high-order harmonic generation (HHG) resulting in measured soft x-ray (SXR) spectra up to 200 eV photon energy. In the first presented experiment, the quantum-mechanical part of the electron-electron interaction, the exchange interaction, is controlled by perturbing gaseous SF6 molecules with SWIR pulses of variable intensity ( 2.2×1014 W/cm2) [1]. A simultaneous HHG probe of the sulfur L2,3 absorption edge reveals a change in the relative oscillator strengths within a spin-orbit-split doublet resonance. We trace this branching-ratio [2,3] alteration back to an exchange-energy increase of up to 50% by employing a theoretical toy-model. These findings are further supported by an ab-initio quantum many-body calculation based on the QUANTY code [4]. In a second experiment, time-resolved x-ray absorption spectroscopy is used to elucidate vibrational molecular dynamics in the perturbative limit. Here, the SWIR pulse precedes the SXR and induces molecular vibrations via nonresonant impulsive stimulated Raman excitation. XTAS can trace vibrational dynamics as imprinted in the resonance-energy shift due to the different involved potential energy curves [5]. In our experiment, we were capable of inducing and measuring the fundamental vibrational breathing mode (period of T = 43 fs) within an ensemble of SF6 molecules with an amplitude of only 50 fm and an unprecedented precision of 14 fm [6]. With the help of a combined quantum many-body and classical simulation, the electronic signature in temporal overlap can be disentangled from the vibrational one and electronic-vibrational coupling dynamics are analyzed.
These XTAS studies pave the way for new ultrafast chemical control schemes as well as molecular vibrational precision metrology.

[1] Rupprecht, et al. Laser control of electronic exchange interaction within a molecule. Phys. Rev. Lett. 128, 153001 (2022).
[2] Onodera, Toyozawa. Excitons in alkali halides. J. Phys. Soc. Jpn. 22, 833 (1967).
[3] Thole, van der Laan. Branching ratio in x-ray absorption spectroscopy. Phys. Rev. B 38, 3158 (1988).
[4] M.W. Haverkort, et al. Multiplet ligand-field theory using Wannier orbitals, Phys. Rev. B 85, 165113 (2012).
[5] Hosler, Leone. Characterization of vibrational wave packets by core-level high-harmonic transient absorption spectroscopy. Phys. Rev. A 88, 023420 (2013).
[6] Rupprecht, et al. Resolving vibrations in a polyatomic molecule with femtometer precision. arXiv 2207.01290 (2022).

Chair: Andreas Buchleitner

18.10.2022 – Jennifer Meyer, TU Kaiserslautern

Reactive scattering of ion molecule reactions for disentangling chemical reactivity

Reaction dynamics open a window into the fundamental process of a elementary reactions, namely the reactive collision. Understanding chemistry at this level will help us to derive detailed structure reactivity relations with the final aim at controlling chemical reactivity in a bottom up approach. We use gas phase methods to study the intrinsic atomistic dynamics of chemical reactions, i.e. how atoms rearrange during the chemical reaction. Our experimental approach uses a combination of crossed beams with 3D velocity map imaging to record energy and angle differential cross sections of ion molecule reactions [1].

Here, I will present two studies on reactions, each with its individual challenges. The first reaction studies the reaction between F and CH3CH2Cl. One of the most studied competition in physical organic chemistry is the one between bimolecular nucleophlic substitution SN2 and elimination E2  due to the importance of both mechanisms in chemical synthesis. The challenge of disentangling these reaction pathways lies in the fact, that the same ionic product is formed which requires methods beyond standard mass spectrometry [2]. The second reaction involves transition metal ions, which due their complex electronic structure are a challenge to experiment and theory alike. I will present first results from our new 3D crossed beam velocity map imaging experiment at Kaiserslautern on the oxygen atom transfer (OAT) reaction Ta+ + CO2 ® TaO+ + CO. The OAT reaction between Ta+ and CO2 is exothermic but spin forbidden in the electronic ground state but spin allowed for the first electronically excited state. Yet, the reaction was found to almost proceed with collision rate at room temperature [3]. This requires the reaction to efficiently cross from the quintet surface over to the triplet surface. Our aim is to identify dynamic signatures related to effects from individual electronic states in either reactants or products.

[1] J. Meyer, R. Wester, Annu. Rev. Phys. Chem. 2017, 68, 333;
[2] J. Meyer, V. Tatji, E. Carrascosa, T. Gyori, M. Stei, T. Michaelsen, B. Bastian, G. Czakó, R. Wester, Nat. Chem. 2021, 13, 977;
[3] G. K. Koyanagi, D. K. Bohme, J. Phys. Chem. A 2006, 110, 1232;

https://www.chemie.uni-kl.de/meyer/seite

Chair: Tobias Sixt