Ions métalliques monochargés, solvatés par des molécules d'eau : Collision et Photofragmentation

Abstract : Solvation has a determining importance in the reactivity of cationic metals. Its understanding goes, among others, through the characterization of the interaction between the ions and bulk solvent. A possible approach, which is followed in this PhD thesis, is to study the energy and the structure of clusters constituted of an ion metal core surrounded by several solvent molecules. The present PhD work reports on the cationic singly charged M(H2O)n+ clusters, with M=Fe,Co,Au and n=1...10, created by coupling the laser vaporization of a metallic rod with a supersonic expansion. Collision induced dissociation of those clusters by He and Ne provides both with threshold energies of fragmentation and cross sections. This study has been performed using a time-of-flight spectrometer operating with a double pulse Wiley-McLaren like setup, which allowed us to vary the collision energy at constant mass resolution. Molecular dynamics calculations have been performed to understand and to modelize the energy transfer between clusters and He. These calculations have allowed us to extract binding energies from the experimental results and to propose a fragmentation mechanism. Photofragmentation results on the same clusters have been interpreted thanks to the picture provided by the collisonnal results. This work revealed the existence of several structures for most of the clusters, in particular, filamentary species, i.e. metastable species with water molecules on external shells even when the first one is not full. Proportions of the different structures have been determined by the number of water molecules on the first solvation shell. The study of metastable species permits a complete exploration also a good knowledge of the metalic ion – solvent potential energy surface.
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Autre. Université Paris Sud - Paris XI, 2001. Français
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L. Poisson. Ions métalliques monochargés, solvatés par des molécules d'eau : Collision et Photofragmentation. Autre. Université Paris Sud - Paris XI, 2001. Français. 〈tel-00007079〉

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