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Dynamique de fragmentation induite par collision de petits agrégats métalliques

Abstract : The goal of this work is the complete analysis of the fragmentation of alkali clusters (Na_n^+ (n < 10), NaK^+ and K_2^+) induced by collision with light atomic (He) or molecular (H_2) targets. The main point is to study how the energy is transmitted to the cluster during the collision and how this energy is shared among the various degrees of freedom of the system and leads to its fragmentation. Two types of interactions govern the collision induced dissociation processes: on one hand, the electronic mechanisms where the target perturbs the electronic cloud and brings the molecule into a dissociative state, and on the other hand, the impulsive mechanisms where the momentum transferred to the atomic cores leads to the rovibrational dissociation of the molecule. The experimental procedure is based on the measurement of the velocity vectors of the outgoing fragments detected in coincidence. This allows to reconstruct the full kinematics of the fragmentation and to separate and characterize for the first time the two types of interactions. The two basic mechanisms of collision induced dissociation are then clearly resolved for the diatomic molecule Na_2+. For the heteronuclear molecular ion NaK^+, it is shown that the dissociation process is due to a combination of electronic and impulsive mechanisms in some of the dissociation pathways. The extension to the study of metallic clusters Na_n^+ (n < 10) fragmentation shows the role and the relative importance of the electronic and impulsive mechanisms and their evolution with the cluster size. The complete analysis of Na_3^+ multi-fragmentation is also presented.
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Yan Picard. Dynamique de fragmentation induite par collision de petits agrégats métalliques. Physique Atomique [physics.atom-ph]. Université Paris Sud - Paris XI, 1999. Français. ⟨tel-00008482⟩

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