Rates of photon induced, metal Ion assisted, unimolecular decomposition of gaseous organometallic complexes using a custom built molecular beam apparatus.
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Dee, S. Jason (Scott Jason)
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This dissertation will focus on the development of a novel technique to study the kinetics and dynamics of transition metal ion assisted σ-bond activation of gaseous organic molecules. The measurements reported represent the first direct experimental determination of reaction kinetics of type: M⁺ + CnHmCO → M⁺CO + CnHm where M⁺ represented a transition metal ion and the organic molecule is often a ketone or aldehyde. The dissociation process is activated by the metal ion and such reactions occur with internal energies significantly less than that required to break C-C or C-H single bonds in isolated organic molecules. Determination of the ion/molecule (and the corresponding isotopic variants) reaction rate constants, over ranges of internal energies, yield information about the dynamics of the reaction mechanism. Rate constants are extracted from the photon-induced decomposition of Ni⁺(Acetone), Ni⁺(d₆-Acetone), and Ni⁺(Acetaldehyde) into Ni⁺CO. A custom-built molecular beam apparatus is constructed to study rates of photon-induced unimolecular decomposition of jet-cooled ionic molecular complexes. The complexes are generated in a pulsed system in which a seeded carrier gas entrains liberated metal ions in a supersonic expansion. The metal ions are created through laser ablation of a metal rod at the throat of a supersonic expansion using photons from a KrF GAM Ex5 Excimer laser. The jet-cooled molecular beam is collimated to extract the coldest portion of the molecular beam. The ions in the molecular beam are then orthogonally accelerated down a TOF-MS. Photons intersect the molecular beam prior to orthogonal extraction, resulting in fragmentation of the ionic complexes. A hemispherical kinetic energy analyzer is used to separate these fragmented complexes from their respective precursor complex. Rates of decomposition are extracted from these studies. Direct measurement of the reaction kinetics over a range of energies yields information about the rate-limiting step in the dissociative mechanism. Optimization of the parameters involved in the construction of the molecular beam apparatus will also be discussed.