Research

 

Photo‐electron spectroscopy and photo‐electron circular dichroism of cold chiral anions

Photoelectron Circular Dichroism (PECD) is a method of chiral discrimination, which can aid in our fundamental understanding of electron dynamics and holds promise for future analytical techniques of chiral compounds. In PECD, irradiation of a non-racemic sample by circularly polarized light, resulting in the detachment of an electron, leads to a forward-backward asymmetry of the photoelectron angular distribution. This technique has significant advantages over other optical CD methods, such as absorption circular dichroism, as sensitivity to the molecular chirality can manifest within the electric-dipole approximation, bypassing the need for observation of weak interactions with a molecule’s magnetic moment. Anions can be mass selected and, as their electron binding energies are usually significantly lower compared to the ionization energies of neutral molecules, more common laser sources in the visible or UV spectral region can be used for the photodetachment. Thus, anion PECD spectroscopy may potentially evolve to a robust analytical tool for chiral discrimination of multicomponent gas-phase samples.

Ionization spectroscopy of gas-phase diatomic molecules

While diatomic molecules may at first sight appear to be comparatively simple systems, some of them possess complex electronic structures and unusual properties such as near-diagonal Frank-Condon matrices and the ability to form by associative ionization. The spectroscopic study of diatomics in the gas phase is of high astrochemical relevance, as it enables detection in space, and also improves the understanding of chemical reactions such as those that lead to the growth of polyatomic molecules.  
We study such molecules using resonance enhanced multi photon ionization (REMPI) spectroscopy, a technique that consists of driving consecutive electronic transitions in a neutral molecule, with photons of known energy, until the total energy exceeds the ionization threshold. From this, accurate, rotationally resolved spectroscopic data is obtained, which can be used for comparison to astrophysical spectra, or for benchmarking quantum-chemical calculations, among others.
In addition, Rydberg states often play an important role in these measurements, since their detection and identification leads to very accurate ionization energies and to spectroscopic data on the respective molecular cation.

IR-UV spectroscopy for studying structure and dynamics of gas-phase clusters

Understanding the structure, chemical behaviour, and dynamics of strongly bound clusters is a central topic of our research. In the last years our molecular beam cluster experiment that is coupled to the beamline of the FHI-FEL has been extended with a laser system that now allows to apply a variety of approaches for the (vibrational) spectroscopy of neutral clusters and small metal-containing molecules using different REMPI schemes and (V)UV single-photon near-threshold ionization.