Studies of reaction mechanism of selected ions in the gas phase using mass spectrometry and computational methods.

摘要

Collision-induced dissociation (CID) of enolic acetone cation, carbon dioxide molecular cation, benzene molecular cation and nitrobenzene molecular have been studied using the Delaware crossed-beam tandem mass spectrometer to understand the detailed molecular dynamics of CID processes of polyatomic ions. Electronic excitation was found to play a major role in the CID of enolic acetone ion. The reaction coordinate for McLafferty rearrangement was calculated by ab-initio methods. The reaction was found to have two steps. Rates of dissociation of 2-hexanone and internal energy of enolic acetone distribution of enolic acetone was calculated using RRKM methods and experimental results were explained based on these calculations.; Dissociation of carbon dioxide ions was found to follow knock out kinematics. Excited states were found to play a major role in the dissociation of carbon dioxide ions. Dissociation of benzene ion was studied at low energies. The mechanism of dissociation of benzene ion was found to be impulsive at all energies. Higher energy pathways an d ring opening reactions were found to be favored in the dissociation of benzene ions. Loss of NO₂ dominated the CID of nitrobenzene ions at all energies studied.; The dissociation of four para-substituted nitroaromatic compounds were explored by tandem mass spectrometry. Electron-donating groups were found to favor isomerization of the -NO₂ group to -ONO followed by loss of NO. Electron-withdrawing groups were found to favor direct homolysis of the C-NO₂ bond with loss of NO₂.