Title:
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Elucidating the structures of cationic metal-nitrous oxide complexes using infrared action spectroscopy
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Gas-phase metal ion-molecule complexes provide model environments within which to study fundamental molecular interactions involved in ligand activation and metal ion solvation. These complexes also represent entrance-channel species for catalytic reactions. The ligand of interest in this thesis is nitrous oxide, which accounts for 5% of anthropogenic emissions and is a potent greenhouse gas with a warming potential 300 times greater than carbon dioxide. Thus, there is considerable interest in reducing N2O emissions particularly via metal-catalysed N2O reduction. M+/0/-(N2O)n complexes represent entrance-channel species for such reactions and yet, little attention has been given to the structures of M+/0/-(N2O)n complexes. This thesis presents the first experimental investigation on M+$(N2O)n and M+n(N2O) complexes studied via infrared action spectroscopy. The infrared spectra are further interpreted and assigned from simulated spectra based on density functional theory (DFT). A range of M+(N2O)n complexes (M = group 11, group 9, and Li, Al) have been studied in an attempt to draw comparisons between the different M+ electron configurations d10, d8, and closed s-shell, respectively). Spectroscopic signatures for N- and O-bound N2O ligands are observed in all cases however the importance of low-lying electronic states is revealed for the group 9 cations, and insertion complexes inferred for the Li+ ion. Infrared multi-photon dissociation (IRMPD) studies on M+n(N2O) complexes (M = Au, Co) also present N- and O-bound spectroscopic signatures. However, as the metal cluster size increases, N2O binds preferentially via the terminal N-atom. Larger clusters represent a more effective energy "bath" facilitating annealing to the lowest energy structure.
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