Study of collisions between low-energy multi-charged ions and Van-der-Waals dimers

Within this thesis, the dynamics of collisions between low energy multi-charged ions and Van-der-Waals dimers is investigated theoretically and experimentally. During the interaction ion/dimer, electrons from the target can be captured by the projectile and produce ionic states of the dimer. These states will then relax into charged fragments via multiple dissociation processes. Experimentally, this study is performed by means of Cold-Target Recoil-Ion Momentum Spectroscopy, a powerful technique which allows the multi-coincidence detection of target ionic fragments and the projectile. Theoretically, the collision dynamics is investigated using a classical calculation based on the Coulombic Over-Barrier Model and adapted to treat diatomic molecules such as dimers. This model has shown good agreement with the experimental results, both in terms of relative production of the different dissociation processes, and in terms of angular dependence of the molecular orientation in respect with the scattered projectile direction. All of this work has finally enabled to provide, for the different processes, the two-dimensional probability maps p(vector(b)) in the molecular frame and to highlight a new relaxation mechanism of the molecular ion named Interatomic Coulombic Decay. This relaxation process is electron emitter of very low energy and could have a significant role in the assessment of damage caused by ion impact. (author)