Doctor of Philosophy
Moore, David T.
Other advisers/committee members
Ferguson, Gregory S.; Roberts, James E.; Strandwitz, Nicholas C.
This dissertation presents work performed using the counter ion co-deposition technique to deposit ions in a controlled manner for matrix-isolation spectroscopy experiments. Matrix-isolation experiments involving ionic species require that both anions and cations be present in the matrix, which the counter ion co-deposition technique achieves by externally generating separate beams of anions and cations, combining them in a quadrupole bender, and co-depositing the combined ion beam with a cryogenic matrix. The conditions under which ions are deposited into a cryogenic matrix can significantly impact the formation and behavior of the resulting ionic species observed in the matrix. These results provide insights into the mechanism by which matrix-isolated species are formed. This dissertation presents results examining the behavior of matrix-isolated species formed in CO2 and CO-doped matrices formed following co-deposition of ions under a variety of experimental conditions. Co-deposition of Cu- with a counter cation in a CO2-doped matrix produces CuCO2- and a number of ionic nonmetal CO2 species. Ionic CO2 complexes, which have been previously observed in argon and neon matrices, are identified in nitrogen and krypton matrices for the first time. High-energy deposition of Ar+ without a specific anionic counter ion alters the behavior of the ionic CO2 complexes. These experiments reveal that two anionic CO2 dimers, (CO2)(CO2-) and C2O4-, undergo a reversible conversion with temperature, and analysis shows the two species are in thermodynamic equilibrium. A complete kinetic analysis of the system was performed, and the thermodynamic and kinetic characterizations of the system produced results in agreement with one another. The equilibrium process is endothermic and driven by a substantial increase in entropy. The exact nature of the entropy increase is yet to be understood, but may arise from the surrounding matrix environment, rather than the two species involved in the equilibrium. Comparison of the system with existing gas-phase studies provided interesting insight into the role of the matrix in the stabilization of the dimeric CO2 anions. The formation of matrix-isolated copper carbonyl anions following deposition of Cu- and Ar+ into a CO-doped argon matrix had a strong dependence on the temperature at which the matrix was deposited. At constant CO concentration, lower deposition temperatures favored the formation of CuCO-, while high temperatures favor the formation of Cu(CO)3-. This behavior appears to be a result of the rate at which deposited species become trapped in the matrix. Lower deposition temperatures result in more efficient trapping, which prevents the formation of highly coordinated copper carbonyls and solvation complexes. The final results presented in this dissertation are of initial experiments performed following an improvement of the counter ion co-deposition system to allow simultaneous mass resolution of both the anionic and cationic beam. The addition of a second mass resolving quadrupole allowed the use of more complex counter ion gases while maintaining the desired level on control over ionic species deposited in the matrix. A single ionization product of a gas that fragments upon ionization can now be selected for deposition. For the first time, with the counter ion co-deposition system, a specific IR active counter ion could be deposited, so there are both anionic and cationic spectroscopic signatures in the matrix following deposition. The presence of a cationic spectroscopic signature allowed clear tracking of the fate of electrons in photolysis experiments. Photodetached electrons from anionic species combined with the cation in the matrix, producing its neutral analogue. Future experiments should make use of the expanded capabilities of the counter ion co-deposition instrument, including the potential to generate complex cations in a chemical ionization source, as well as generating anions in the chemical ionization source allowing for co-deposition experiments of metal cations.
Goodrich, Michael Edward, "Matrix-Isolation Studies of Ionic CO2 Clusters and Improvements on the Counter Ion Co-Deposition Technique" (2017). Theses and Dissertations. 2607.