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This research project set out to shed light at the ammoniated electron by investigating the electron binding motifs of excess electrons attached to ammonia clusters. During, the first year small ammonia cluster anions were investigated with ab initio methods, resulting in predictions of small, so far undetected cluster anions, and a set of reference data for developing electron-ammonia potentials. Moreover, a second major project, a collaboration with an organic chemist regarding the mechanisms of reactions of N-oxime ethers, was started, since the originally proposed project turned out to be less suitable for undergraduate researchers than initially anticipated.

In the second year the project developed into a much broader investigation of negatively charged anions. One reason is that developing reliable electron-ammonia potentials turned out to be a major challenge, and the second reason is again suitability for undergraduate researchers. Briefly, the goal was to develop an electron-ammonia potential that would (1) reproduce ab initio binding energies, (2) reproduce ab initio electron distributions, and (3) be computationally inexpensive. So far we have not reached this goal, and after much work it still seems that one can have only two out of the three. This research remains for the time being unpublished. However, the lack of success convinced me that taking a broader perspective, looking at other cluster anions, and approaching the problem of building reliable and fast electron-molecule potentials from a more general point of view, was a good idea. This work consists of three major projects that each led to a publication.

The first project deals with the efficient computation of electron molecule interactions and their derivatives. What was needed was a software infrastructure that allows researchers to implement new potentials for new molecules in a simple way, and that then takes care of computing the wavefunction of the excess electron, the electron binding energy (and its derivative). To this end I started a collaborative effort with Ken Jordan at the University of Pittsburgh and Levent Yilmaz at the Pittsburgh Simulation and Modeling Center. The result is the Pisces code which is still under heavy development, but which already includes potentials for excess electrons bound to water or sodium chloride clusters, and that can be easily extended to ammonia clusters and mixed systems. Moreover, the code parallelizes well, and our studies show that it is suitable for simulating larger cluster anions.

The second project deals with excess electrons attached to NaCl clusters. NaCl clusters form the high-polarity end of a continuum of closed-shell clusters where the opposite “unpolar” end is represented by rare gas clusters, and water and ammonia clusters fall somewhere into the middle. NaCl cluster anions were a very active research topic in the 1990ties, and my student Bijay Bhattarai and I were very surprised when we found new isomers of clusters as small as the trimer and the tetramer that for the tetramer even turned out to be far more stable than the most stable isomer known so far. In view of these surprising results we started a collaboration with Lenz Cederbaum at the University of Heidelberg who checked our findings with an independent method. The combined results shed new light on electron binding motifs dominated by polarization interactions, and allowed us to critically examine the models developed earlier.

The third project connects directly with the observation of delayed electron emission from aluminum cluster anions kept in electrostatic ion traps. In contrast to ammonium or sodium chloride clusters, aluminum clusters have an open-shell electronic structure, and both the neutral and the negatively charged clusters show strong mixing between different electronic configurations. The results of this project are a better understanding of the photoelectron spectra of aluminum cluster anions and of the mechanisms leading to rapid radiative cooling in ion traps.

All in all this grant made a very positive impact on my carrier well beyond the scientific results per se and the associated publication record. I have been able to start an ambitious independent research program -instead of dabbling with toy problems aimed primarily at providing a research experience for students- and I have been able to start and maintain collaborations with internationally respected researchers at major universities. Moreover, I have been able to establish a track record of performing high quality research at an undergraduate institution, that is, to show that even though my paper-production-frequency is smaller than that of research university professors, my research itself can be held to the same standards as the work done at research universities. The same is true for my students. It makes a big difference to them to know that they are participating in projects that have a good chance to lead to a publication in a proper research journal, and to see that researchers from major institutions are interested in the posters they present.