The Scientific Program

 

In the following we give a short synopsis of the scientific projects carried out within this research unit, of their synergies and of the interaction between the research teams. The work can be grouped in the following categories:

 

 

Time resolved experiments:

 

From a fundamental viewpoint, a direct view of ICD in the time domain is most important. Two projects, by the Frühling and Jahnke groups, address this topic experimentally. Both plan to use time-resolved electron emission by using streaking fields in the THz domain, but are very different with respect to the detection schemes. Straight-forward electron spectroscopy, as proposed by the Frühling group, has been demonstrated for photoelectrons and is applicable to clusters of any size. The Jahnke group is planning to mate the streaking technique with COLTRIMS detection. This might be restricted to very small clusters, but will pave the way for conceptually novel experiments on electron dynamics in general. Simulations of time resolved ICD spectra will be done by the Averbukh group. The spectroscopic characterization of systems chosen for time resolved experiments will be done by conventional electron spectroscopy in cooperation with the Hergenhahn group.

 

 

Dynamics driven by ICD and competition with molecular dynamics:

 

The Coulomb explosion caused by ICD leads to a molecular dynamics, which so far has only been studied in dimers. Moreover, in a lot of molecular systems some of the initial states giving rise to ICD are dissociative on the level of an isolated molecule. This leads to an interesting competition between intrinsic molecular dynamics and ICD. The Dörner group will use COLTRIMS to elucidate these phenomena by recording the momenta of the charged fragments. These experiments will be closely accompanied by molecular dynamics simulations of Nicolas Sisourat and coworkers. Fragment dynamics of some of the same systems will also be recorded by the Denifl group, but using electron impact instead of photoionization to initiate ICD.

 

 

ICD and resonant Auger decay:

 

The Auger-like autoionization of core-excited states, termed resonant Auger decay, has amply been studied in isolated atoms and molecules. In the context of this research group, resonant Auger decay is of interest in two respects: 1. In rare gas systems, ICD is expected to occur as a cascade process after local resonant Auger decay. As the resonant excitation which thus initiates ICD is highly localized, this has the potential to become a method of materials analysis. 2. In hydrogen bonded systems, ICD-like decay amplitudes might already occur in core level decay. We address these questions in the projects of Dörner (rare gas dimers), Hergenhahn (rare gas clusters), Gokhberg (benchmark calculations) and Winter (hydrogen bonded systems).

 

 

ICD after electron impact and electron capture:

 

Studies on ICD so far almost exclusively have used excitation by photons. To broaden the knowledge on this phenomenon we have included the Innsbruck group (Denifl) in this collaboration, who have enormous expertise in electron impact experiments on clusters. They will study both ICD after electron impact and autoionization after electron capture (ICEC) in two independent projects. Results can be compared to calculations (Gokhberg/Cederbaum) and photon driven experiments on the same systems (Hergenhahn).

 

 

ICD of solvated biomolecules and other solvation systems:

 

We plan to study the occurrence of ICD in biologically relevant systems. Experimentally, we will use a bottom-up approach by studying microsolvation clusters of biomolecules (Hergenhahn), and solvated biomolecules in a liquid jet (Winter). Also for the studies of solvation systems outside of a biological context ICD will be of importance (solvent geometries, charge transfer), see application of the Winter group. Methodological developments for simulations of ICD in these large systems, and simulations, will be done in the Dreuw group, using know-how of the Gokhberg/Cederbaum group to implement the treatment of the electron continuum. Simulations of Andreas Dreuw and coworkers will also identify biological systems in which ICD is of relevance. Doped He droplets are an exotic type of solvation system of great current interest, and will be studied in the Denifl group.