Analysis of metastable decays with mass spectroscopy

Within the Charlotte Bühler Habilitationsstipendiums we plan to measure decay reactions of molecular and cluster ions as a function of time using a three sector field mass spectrometer. In particular the produced fragment ions are analysed in terms of mass, charge and kinetic energy. The high resolution kinetic energy release distributions form the basis of further investigations. For small molecules as for example rare gas dimer ions we can identify specific transitions within the molecular system if accurate potential energy curves, including spin-orbit interactions, are available. The method used here to detect and identify transitions of excited states by means of a mass spectrometer constitutes an alternative to spectroscopic tools and thus allows an independent way to check calculated potential energy curves. It is interesting to note that even very small variations in the calculated curves produce quite different kinetic energy release distributions. Hence it is possible to discuss the accuracy of calculated curves within a few meV. For argon and neon dimers we could finish the experimental studies as well as the computations of the transition probabilities and resulting kinetic energy release distributions successfully, whereas for xenon- and krypton dimers we are not only working on more accurate data but also on the interpretation of these data. In addition we want to examine the stability of larger cluster ions, which we could not study before due to a lack of mass resolution. Now with the three sector field machine we are able to investigate also systems, which have several natural isotopes, as for example neon or krypton, because the selection of parent ions with the high resolution two sector field mass spectrometers enables an unambiguous selection. Here we want to measure first kinetic energy release distributions and secondly use statistical theories to extract from these data the binding energies of the decaying systems. In the case of C60, the most famous carbon cluster, it became clear only recently that some open questions can only be solved, if the parent ions can be selected isotopically resolved.