Multidimensionale interferometrische Photoelektronenspektroskopie mit XUV-Photonen (MULTIPLEX)

Photochemical processes play a crucial role in nature. Yet, understanding the underlying molecular dynamics remains a challenge. One difficulty arises from the vast number of intra- and inter-molecular degrees of freedom in molecular systems. In particular, electronic-vibrational couplings and environmental perturbations lead to a complex and highly convoluted response. Another difficulty is caused by the ultrafast (pico to few femtosecond time scales) and predominantly non-radiative conversion/relaxation processes involved in photochemical reactions. Special spectroscopy methods are required to detect and resolve the molecular dynamics in real time. This combination of challenges makes it hard to unravel the primary mechanisms that drive photochemical processes in molecules.

In this project, we develop a unique experimental method to address these issues. To reduce the complexity of the molecular systems, we focus on small quantum systems consisting of only single molecules up to small molecular complexes forming the functional sub-unit of larger systems. These units are isolated in ultrahigh vacuum to assure clean conditions and minimum environmental perturbations. To address the spectroscopic challenges, we apply time-resolved photoelectron spectroscopy (TRPES). Advantages of TRPES are the elimination of dark states, the sensitivity for electronic and nuclear dynamics and the high time resolution. This combination of features makes TRPES the ideal method to study photochemical processes in molecules

So far, TRPES was mainly limited to UV ionization sources. However, the low energy of UV photons strongly limits the observation window in the photoelectron spectra. This situation is sketched in figure 1. In our project, we use extreme ultraviolet (XUV) ionization pulses from a tabletop XUV light source to solve this problem. In addition, we adapt concepts from multidimensional nuclear magnetic resonance spectroscopy and optical 2D spectroscopy to strongly increase the resolution and the disentanglement of the photoelectron spectra. This combination of techniques forms a new spectroscopic method featuring the gap-less mapping of molecular reactions with high time and energy resolution.

Figure 1: XUV TRPES of photochemical reactions in molecules. The reactant is optically excited followed by a relaxation either into new molecular configurations or back to the ground state. UV ionization will offer only a limited observation window of the molecular dynamics as opposed to an XUV probe. MULTIPLEX will provide gap-less mapping of the electronic-nuclear dynamics with high temporal and spectral resolution.

For open positions in this project see postings here.

Project leader:
Dr. Lukas Bruder, lukas.bruder[at]physik.uni-freiburg.de

Funding:

European research council: Starting Grant 101078689 MULTIPLEX

Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them.

Baden-Württemberg Stiftung Elite Postdoc Programm

Research training group DynCAM (RTG 2717)