Licentiate Thesis: Fragmentation of fullerenes and water embedded biomolecules

by Nicole Haag (Stockholm University, Department of Physics)

Friday 19 Sept 2008, 14:00 → 16:00 Europe/Stockholm

FA31

This thesis includes two studies on different complex molecular systems: (i) multiply charged fullerenes and (ii) adenosine 5'-monophosphate (AMP) with different numbers of attached water molecules. Collision experiments have been performed in order to investigate the relations between energy deposition and fragmentation and to shed light on the mechanisms behind energy and electron transfer processes in collision reactions in general. In (i), the fragmentation of fullerenes following multiple ionization by collisions with slow highly charged ions has been studied with focus on the asymmetric fission processes Cq+60 ->C(q-1)+58 + C+2 and Cq+70 -> C(q-1)+68 + C+2. For these reactions, a systematic study of experimental kinetic energy release distributions (KERD) is presented for mother ions in charge states q=4-8. In addition, we use the measured branching ratios between asymmetric fission and evaporation of a neutral C2 unit to deduce semi-empirical values for the fission barrier heights by means of a statistical approach. In (ii), electron capture processes in collisions between nanosolvated AMP anions and neutral sodium atoms have been studied. We find that dianion formation always leads to water evaporation and fragmentation of the AMP in the form of loss of a single hydrogen atom. This damaging effect occurs regardless of the number of water molecules initially attached to the parent ion, and becomes more important as the size of the water nanodroplet increases. This is just the opposite to the protective effect of attached water molecules observed for collision induced dissociation processes without electron transfer.