Expected Results

 

In the short to medium term we expect to carry out a number of key experiments on ICD which are extensions of the current state-of-the-art in the field. Examples are:

 

  1. A demonstration of ICD in solvated biomolecules, with energy transfer between the molecule and its solvent shell.

     

  2. A time-resolved experiment on ICD.

     

  3. A comparison of ICD of the same vacancy state but initiated by different excitation mechanisms, e.g. photon absorption vs. electron impact.

     

  4. A demonstration of the opening and closing of ICD channels by manipulation of the chemical environment of the participating centres, e.g. by a change of the pH value of a solution.

     

  5. Theoretical and experimental evidence of resonant Auger driven ICD, which will allow to selectively address, by selecting the photon energy, individual atoms and surface or bulk sites.

 

More examples for the expected findings can be found in the project descriptions. In the longer term advances are expected in a number of areas.

 

Physics

In physics ICD is one example of an ultrafast process, for which until recently it was not possible to perform time-resolved measurements at all. Meanwhile experiments in the range of femto- and even attoseconds have been carried out and one has begun to understand the correlated dynamics of electrons and nuclei in molecules. This has only been possible because at the same time the theoretical description of these phenomena has made huge progress. Also for ICD, a deeper insight in the process is only possible if we try and understand it in a time-dependent picture [14][15]. Turning this around, ICD is an excellent example for one of the 'big' questions which is invoked by ultrafast quantum-mechanical experiments or theory: What is the time scale at which electron correlation sets in, in a multi- particle system?

 

Chemistry

In the area of chemistry it is of great interest that ICD only proceeds because of the chemical environment of the centre that is initially ionized. Thus, an investigation of the existence of ICD, its intensity and its decay energies can answer questions on solvent geometries in unordered systems, which cannot be resolved by other methods. The decay rate of ICD depends strongly on the distance of the two participating systems, in a simple model as R-6. A comparison of ICD spectra in different situations will therefore reveal even small differences in geometry. The energy differences which drive ICD are small. Comparatively small changes in the electronic energies of the participating initial and final states can therefore be relevant, depending on whether in a given system a certain ICD channel is open or closed. The investigation of this control mechanism is one of the long-term perspectives of the research unit.

 

Biochemistry

In the area of chemistry it is of great interest that ICD only proceeds because of the chemical environment of the centre that is initially ionized. Thus, an investigation of the existence of ICD, its intensity and its decay energies can answer questions on solvent geometries in unordered systems, which cannot be resolved by other methods. The decay rate of ICD depends strongly on the distance of the two participating systems, in a simple model as R-6. A comparison of ICD spectra in different situations will therefore reveal even small differences in geometry. The energy differences which drive ICD are small. Comparatively small changes in the electronic energies of the participating initial and final states can therefore be relevant, depending on whether in a given system a certain ICD channel is open or closed. The investigation of this control mechanism is one of the long-term perspectives of the research unit.

 

We expect ICD to be an important reaction mechanism on surfaces, e.g. condensed rare gases or – more importantly – wet surfaces. Although also the cluster and liquid jet experi- ments suggested in this Research Unit arguably probe surface effects of their respective targets, experiments which address ICD on the surfaces of bulk condensed matter can address different problems and will have a great potential. (Incidentally, the first such experiment has just been reported [16]) Several of the groups in this Research Unit already carry out condensed matter experiments in other contexts (Dörner group, Innsbruck group) or plan to do so in collaboration with experts in that field (Hergenhahn group). Experiments on ICD at surfaces can be expected in the second phase of this Research Unit.

 

Finally we would like to emphasize the potential importance of ICD-related processes, which proceed by a sequence of electron capture - energy transfer - electron emission [9] (Intermolecular Coulomb Electron Capture, ICEC) and which will be investigated by the Research Unit both in theory and in experiments. Here the experiment will be performed by the Denifl group, the theory will by done by the Gokhberg/Cederbaum group (theory funded externally to this research unit). We expect to demonstrate this process experimentally, and we will develop computational methods for ICEC in realistic systems. This will enable us to propose suitable experiments and to exploit its potential e.g. for tailoring the charge transfer properties of complex systems. Along the same line we expect that experiment and theory of ICD driven by the resonant Auger effect will have considerable impact as this is a resonant process where the very high photon energy resolution of today’s radiation sources can be used to selectively address different sites within a system.