Fragment size distributions and caloric curve in collision induced cluster fragmentation

We report on a cluster fragmentation study involving collisions of high‐energy (60 keV/amu) H3+(H2)(m⩽14) hydrogen cluster ions (m = 1,14) with atomic helium. The experimental characterisation of the cluster fragmentation not only by the average fragment size distribution but also by a statistical analysis of the fragmentation events has become possible owing to a developed multi‐coincidence technique in which all the fragments of all collisions occurring in the experiment are mass analysed on an event‐by‐event basis. Measurements and analysis are carried out on a large number of cluster ions prepared at the same total energy, as opposed to observing the evolution of a single system over time (time averaged ergodic hypothesis). By selecting specific decay reactions we can start after the energising collision with a micro‐canonical cluster ion ensemble of fixed excitation energy. From the respective fragment distributions for these selected decay reactions we derive corresponding temperatures of the decayi...