Browsing by Subject "Gas phase."
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Item Construction and calibration of a custom time-of-flight mass spectrometer and its use in measuring the reaction kinetics of transition metal ion-organic interactions.(2009-09-03) Castleberry, Vanessa A.; Bellert, Darrin Joseph, 1968-; Chemistry and Biochemistry.; Baylor University. Dept. of Chemistry and Biochemistry.A unique instrument was constructed and used to generate and interrogate jet cooled neutrals, ions and their respective clusters. The instrument is a result of the artful marriage of supersonic expansions combined with time of flight spectroscopy. Ionization occurs in a large main chamber. The ions are separated via a kinetic energy pulse from a custom built linear particle accelerator. The revelatory hardware for our instrument is a microchannel plate detector (MCP). The MCP is mounted on the exit of a custom designed and built hemispherical energy analyzer (sector), which acts as an energy filter. This filtering characteristic of the sector permits study of selected ionized fragments. To test the instrument, the 2-photon resonant, 3-photon ionization spectrum of gaseous atomic copper was measured. The (n = 9 – 21) Rydberg series was observed in 2-photon excitation. The term energies of this series converged to copper's lowest ionization threshold with an apparent quantum defect of 0.92. The state which couples the ground state of copper to the Rydberg series is a non-stationary state composed primarily of the spin-orbit components of the lowest 2P° atomic states. Additionally, the time dependence of the gaseous unimolecular decomposition of the jet-cooled adduct ion, Ni⁺•Acetone was monitored by selective detection of the daughter fragment, Ni⁺CO. Various photon energies were supplied to initiate dissociation of the adduction. The energies employed in this reaction were well below that required to fragment C-C ς-bonds. First-order unimolecular decomposition rate constants, k(E) ranged from 55000 – 113000 s⁻¹. The rate constants decreased with decreasing amounts of internal excitation. Ni⁺ cation is implicated as a catalytic necessity to activate the bond and cause molecular fragmentation. These experiments represent the first direct kinetic study of such catalytic type reactions.Item Metal ion assisted unimolecular decomposition of gaseous organometallic complexes : acquisition of reaction rate constants and dynamics of the dissociative mechanism.(2011-12-19) Villarroel, Otsmar J.; Bellert, Darrin Joseph, 1968-; Chemistry and Biochemistry.; Baylor University. Dept. of Chemistry and Biochemistry.Reaction rate constants have been acquired for the transition metal ion assisted decomposition of various organic molecules, and their deuterium labeled analogs in the gas phase. The metal ion activates organic bonds and mediates the formation of products. Thus, the transition metal cation lowers the bond activation energy requirements in these decomposition reactions making these systems model for catalysis. Catalytic reaction kinetics are not well understood and it is hoped that the resolved study of simpler catalytic models will further the development of the theoretical tools necessary to describe such mechanistic behavior at the molecular level. Reaction rate constants for these model systems are measured using a custom-built molecular beam apparatus. The clusters are formed under supersonic expansion conditions and are bound by the charge-dipole electrostatic interaction between a transition metal cation and a polar organic molecule. The unimolecular decomposition occurs upon laser photon absorption by the jet-cooled cluster yielding a stable neutral molecule and corresponding ion. This dissertation will focus on the unimolecular decomposition kinetics of the Co⁺-Acetone cluster and its deuterium labeled analog. Rate constants are measured at well resolved cluster internal energies. The kinetic isotope effect (KIE) for each measurement was determined. Results are compared to the similar Ni⁺-Acetone decomposition reactions, where the KIE was also measured. These two similar systems present rather different dissociation dynamics. Arguments based on the electronic structure of each ion explain this unique behavior between these similar systems. DFT calculations are made on most systems presented in this dissertation. The most likely geometries and relative energies of the reactants, intermediates and products are determined. Such information specifies aspects of the reaction coordinate and leads to suggestions of mechanisms. This was primarily applied in the final chapter of this dissertation where preliminary results of Ni⁺-assisted decomposition of cyclopentanone are presented. This system represents the group’s first study of a ring-opening reaction.