Cluster Dynamics
Prof. Dr. Udo Buck

-- Very recently, we succeeded in developing a new method by extending the IR-UV arrangement which allows us to measure size selective IR spectra of water clusters up to n=500. In this way the crystallization was determined to start around n=275 and and to be finished at n=475. The results were published in Science [249]. See also press release MPG.

A new series of experiments was carried out in Göttingen and was combined with the latest theoretical simulations of two groups in the USA. The results provide strong evidence that the end of ice occurs when the clusters are 90 water molecules. Unexpectedly the researchers found in both simulation and experiment that the clusters in this size range oscillate in time between the amorphous and the ice state. The results have been published in the Proceedings of the National Academy of Science USA [257] . This article was given the Cozzarelli Prize as best contribution of the Physical and Mathematical Sciences. See also the press release of the University of Utah UTA.

-- An exciting application of the cluster mass spectra of these system has been the clarification of the results of the Cassini mission on the cryovulcanic plumes of the Enceladus moon of Saturn. The results of the Heidelberg cosmic dust team agree qualitatively with our cluster experiments. Na poor ice particles exhibit Na(H₂O)_n structures, while Na rich grains contain Na(NaOH)_k(H₂O)_n species. The presence of Na is a direct indication of liquid water in the Enceladus. Therefore we repeated the experiment in a liquid beam in the Abel group and observed also the predicted sodium chloride and carbonate salts. The results were published in Nature [237] and found a lot of attention in the press in Germany.