CRC Projects

Goal of this project is to gain a deeper understanding of circular dichroism in the emission of electrons upon the absorption of a single photon. At first we study how systematical changes in the molecular potential affect the scattering of the directly released photoelectron and therefore the ability to shift electron flux in the forward/backward direction, which is well-known as photoelectron circular dichroism. In the next step, we aim for a circular dichroism effect in the emission of fast Auger electrons, released either after resonant or non-resonant photon absorption. The third series of experiments focusses on the question how the photon’s helicity is shared among several emitted electrons (as Auger- and photoelectrons).

Dr. Markus Schöffler 
Goethe-Universität Frankfurt am Main
Fachbereich Physik
Institut für Kernphysik
Max-von-Laue-Straße 1
60438 Frankfurt am Main
Telephone: +49 69 798-47022
Fax: +49 69 798-47024
E-Mail: schoeffler[at]atom.uni-frankfurt[dot]de

We study electron emission from chiral molecules in the strong field, long wavelength regime of tunnel ionization using circularly polarized femtosecond laser pulses. The project has two subprojects; in the first, we will measure the three dimensional momentum distributions of electrons in coincidence with fragment ions using a COLTRIMS Reaction Microscope. In the second subproject we will measure the momentum resolved spin polarization of the electrons emitted from chiral molecules.

Prof. Dr. Reinhard Dörner
Goethe-Universität Frankfurt am Main
Fachbereich Physik
Institut für Kernphysik
Max-von-Laue-Straße 1
60438 Frankfurt am Main
Telephone: +49 69 798-47003
Fax: +49 69 798-47024
E-Mail: doerner[at]atom.uni-frankfurt[dot]de

On chiral molecular prototypes we will address three different ultrafast processes: 1.) We will create an electronic Rydberg wavepacket with circularly polarized light resulting in a Kepler type of orbit. This loosely bound electron will therefore scout different areas of the chiral molecule. Time resolved photoelectron circular dichroism (PECD) will sense these neutral electron dynamics influenced by vibrational dynamics. 2.) We will change the frequency ordering in a white light continuum and investigate how temporal ordering of electronic excitations is reflected in the PECD signal. 3.) We will study PECD from the frozen nuclear configuration limit to the own-state picture limit.

Prof. Dr. Thomas Baumert
Universität Kassel
Institut für Physik
Experimentalphysik III - Femtosekundenspetroskopie
und ultraschnelle Laserkontrolle
Heinrich-Plett-Straße 40
34132 Kassel
Telephone: +49 561 804-4452
Fax: +49 561 804-4453
E-Mail: baumert[at]physik.uni-kassel[dot]de

We will investigate experimentally how the chirality of a molecule evolves during a dissociation process. For how long and under what conditions can the chirality be proven experimentally by time-resolved photoelectron circular dichroism? How may chirality be defined in dissociating systems with chiral or non-chiral fragments? To answer those questions, we will perform pump-probe experiments with split femtosecond X-ray pulses from free-electron lasers and with a combination of picosecond X-ray pulses from synchrotron radiation facilities and UV femtosecond laser pulses. In the dissociation processes we will follow the electrons and the nuclei in their respective time domains.

Prof. Dr. Arno Ehresmann
Telephone: +49 561 8044060
Fax: +49 561 8044510
E-Mail: ehresmann[at]physik.uni-kassel[dot]de

Dr. André Knie
Telephone: +49 561 8044062
Fax: +49 561 8044150
E-Mail: knie[at]physik.uni-kassel[dot]de

Universität Kassel
Institut für Physik
Experimentalphysik IV - Dünne Schichten
und Synchrotronstrahlung
Heinrich-Plett-Straße 40
34132 Kassel

Circular dichroism shows up in the absorption spectra of chiral molecules or in the polarization of transmitted light but also in the ion yield after laser excitation. Any means to change the molecular structure or to influence the effective strength of the electric and magnetic dipole moments should therefore be reflected in the ion yield. From an ultra-fast time dependent perspective, structural changes can be induced and controlled by vibrational wavepacket motion. Effective transition moments may be changed in sequential photon absorption processes or by employing non-perturbative light matter interaction regimes. These approaches will be investigated with the help of ultrafast coherent control techniques.

Prof. Dr. Thomas Baumert
Universität Kassel
Institut für Physik
Experimentalphysik III - Femtosekundenspetroskopie
und ultraschnelle Laserkontrolle
Heinrich-Plett-Straße 40
34132 Kassel
Telephone: +49 561 804-4452
Fax: +49 561 804-4453
E-Mail: baumert[at]physik.uni-kassel[dot]de

The major idea of this project is to use atoms such that the clock transition can be used for chiral identification of molecules. We are using Rydberg states which have extreme properties such as a large electric and magnetic dipole and higher order moments. Additionally, ultra-stable clock states in the same atom allow for quantum-sensing protocols. The phase shifts generated by the interaction with chiral molecules is detected using Ramsey and Spin-Echo pulse sequences, which also refocus phase shifts arising from interactions with the environment.

Prof. Dr. Kilian Singer
Universität Kassel
Institut für Physik
Experimentalphysik I - Licht-Materie-Wechselwirkung
Heinrich-Plett-Straße 40
34132 Kassel
Telephone: +49 561 8044235
E-Mail: ks[at]uni-kassel[dot]de

The two goals of this project are first to explore Coulomb explosion as a tool for chiral recognition and second to combine Coulomb explosion with high energy photoelectron diffraction for chiral recognition. We will follow two routes: firstly we drive the Coulomb explosion by femtosecond laser pulses and secondly we will use synchrotron radiation to charge up the molecule inner shell ionization followed by an Auger cascade. In this case, we will explore, if the combination of fragment detection and detection of a high energy photoelectron enhances the chiral discrimination.

Dr.  Markus Schöffler
Telefon: +49 69 798-47022
Telefax: +49 69 798-47024
E-Mail: schoeffler[at]atom.uni-frankfurt[dot]de

Prof. Dr. Reinhard Dörner
Telefon: +49 69 798-47003
Telefax: +49 69 798-47024
E-Mail: doerner@atom.uni-frankfurt.de

Goethe-Universität Frankfurt
Institut für Kernphysik
Max-von-Laue-Str. 1
60438 Frankfurt am Main

In project B2, we exploit tailored microwave fields to investigate, control, and manipulate chiral molecules in the gas phase based on microwave three-wave mixing. It is a coherent, resonant, and non-linear process and is inherently mixture compatible. It provides access to absolute configuration and enantiomeric excess determination. Using tailored microwave pulses, enantiomer-selective population transfer between states is possible, which is the first step towards enantiomer separation using electromagnetic fields. Such samples are unique starting points for advanced molecular physics experiments, such as chirality-dependent collisions and precision measurements.

Prof. Dr. Melanie Schnell
Telephone: +49 (0)40 8998 6240
E-Mail: melanie.schnell[at]desy[dot]de
Deutsches Elektronen-Synchrotron (DESY)
Notkestraße 85
22607 Hamburg

and

Christian-Albrechts-Universität zu Kiel
Institut für Physikalische Chemie
Max-Eyth-Straße 1
24118 Kiel

In project B3 properties and dynamical behavior of chiral molecules in the gas-phase will be studied by means of infrared- and Terahertz-spectroscopy. The tunneling behavior of chiral molecules as a function of rotational-vibrational excitation will be investigated using narrow-band phase-stabilized infrared lasers. The chiral excess of a racemate will be determined by coherently coupled rotational-vibrational states and methods for enantio-selective excitations will be developed in cooperation with project B2. These investigations, supported by project C3, will open new prospects to chiral purification of a racemic gas-mixture. Furthermore, spectroscopic methods will be developed towards precision spectroscopy to experimentally prove the predicted effect of molecular parity violation for the first time.

Prof. Dr. Thomas Giesen
Universität Kassel
Institut für Physik
Heinrich-Plett-Str. 40
34132 Kassel
Telephone: +49 (0)561 804 4775
E-Mail: t.giesen[at]uni-kassel[dot]de

We aim to understand and control the transformation of an individual chiral molecule from one enantiomer to the other. The work plan is designed to pave the way to achieve the long-term goal of enantiomeric purification of chiral molecules by optical means. Therefore, we will investigate the dynamics induced by excitation of an excited state with achiral geometry in a two-color pump-probe experiment. The probe will be photoelectron circular dichroism (PECD), which is highly sensitive on minor changes in chirality. Later, we will use a time-domain control approach to invert the handedness of an enantiopure sample. These two tasks are accompanied by static reference measurements of our PECD probe on the three chiral molecules under investigation.

Dr. Arne Senftleben
Universität Kassel
Institut für Physik
Heinrich-Plett-Str. 40
34132 Kassel
Telephone: +49 (0)561 804 4294
E-Mail: arne.senftleben[at]uni-kassel[dot]de

The C1 project proposes a comprehensive theoretical investigation of circular dichroism in the inner-shell ionization, fragmentation, and decay, as well as in the multiphoton and tunnel ionization of the partially and fully spatially-oriented chiral molecules. It suggests developments of reliable theoretical approaches for the quantitative description of angle- and time-resolved experiments with chiral molecules. Together with the experiments planned in this CRC, it aims at qualitative understanding, quantitative characterization, and systematic quantification of advanced observables.

Prof. Dr. Philipp Demekhin
Universität Kassel
Institut für Physik
Heinrich-Plett-Str. 40
34132 Kassel
Telephone: +49 (0)561 804 4013
E-Mail: demekhin[at]physik.uni-kassel[dot]de

Photoionization experiments are a prime tool to investigate chirality of molecules in the gas phase. In this project we will develop a time-dependent ab initio description of such experiments, addressing the challenges of an adequate model for the chiral photoelectron continuum and a systematic treatment of electron correlation. Combining this approach with quantum control theory, we seek to determine the ultimate strength of chiral signals that can be obtained with randomly oriented molecules.

Dr. Daniel Reich
Telephone: +49 (0)561 804 4574
E-Mail: daniel.reich[at]physik.uni-kassel[dot]de

Prof. Dr. Christiane Koch
Telephone: +49 (0)561 804 4407
E-Mail: christiane.koch[at]uni-kassel[dot]de

Universität Kassel
Institut für Physik
Heinrich-Plett-Str. 40
34132 Kassel

Molecules of a given handedness require enantiomer-specific chemical synthesis. This project is dedicated to investigating whether and how suitably tailored electromagnetic fields can be used to convert a mixture with molecules of both handednesses into an enantio-pure sample. Enantiomer-selective excitation followed by separation as well as a unidirectional conversion of one enantiomer into the other are possible means towards this goal. Quantum control theory will be employed to derive the shape of the electromagnetic fields that drive the required rotational and vibrational dynamics.

Prof. Dr. Christiane Koch
Universität Kassel
Institut für Physik
Heinrich-Plett-Str. 40
34132 Kassel
Telephone: +49 (0)561 804 4407
E-Mail: christiane.koch[at]uni-kassel[dot]de

Theoretical approaches that take the relevant fundamental interactions into account are developed and applied primarily to i) establish new routes to assign the absolute configuration of chiral molecules in the gas phase based on the detection of high-energy photoelectrons as well as to ii) identify ionic candidate sys-tems and describe their properties to pave the way for successful precision experiments with chiral molecules, which contribute as highly sensitive probes to fundamental physics.

Prof. Dr. Robert Berger
Philipps-Universität Marburg
Fachbereich Chemie
Hans-Meerwein-Str. 4
35032 Marburg
Telephone: +49 (0)6421 28 25687
E-Mail: robert.berger[at]uni-marburg[dot]de

The underlying project provides tailor-made molecules in order to establish structure property relationships between physical parameters related to chirality and structural features on a molecular level. Within the project, we will aim at elucidating the relevance of structural features on the response obtained for the complementary physical methods available in this CRC. As a consequence of the different methodologies two general sets of chiral compounds will be envisaged, one being as small as possible (in terms of number of atoms), the other one featuring chromophoric units to allow for absorption bands in the visible region.

Prof. Dr. Rudolf Pietschnig
Universität Kassel
Institut für Chemie
Heinrich-Plett-Str. 40
34132 Kassel
Telephone: +49 (0)561 804 4615
E-Mail: pietschnig[at]uni-kassel[dot]de

This project is dedicated to all administrative tasks and duties of ELCH as a whole, and represents the CRC to both participating and external institutions. Its tasks primarily cover three major areas: (i) the administration and organization of the CRC itself; (ii) outreach, i.e. public relations and communication to a broader public (iii) early career support, i.e. development of students and young researchers at all stages of education. Measures for the enhancement of gender equality play an important role in all of the above described areas.

Prof. Dr. Thomas Baumert
Universität Kassel
Institut für Physik
Heinrich-Plett-Str. 40
34132 Kassel
Telephone: +49 (0)561 804 4452
E-Mail: baumert[at]physik.uni-kassel[dot]de