THE DEVELOPMENT OF AN ANGLE-RESOLVED MASS SPECTROMETER AND ITS APPLICATION TO ION CHEMISTRY AND REACTION DYNAMICS
Abstract
This thesis takes as its subject, ion/molecule and ion/atom reactions occurring at kiloelectron volt energies; additionally, the unimolecular dissociation of metastable ions was investigated. The investigation of these reactions was accomplished through measurements of ion translational energy. For the bimolecular reactions, a unique form of mass spectrometry was utilized, viz. angle-resolved mass spectrometry. A collision chamber and angle-resolving slit installed in a conventional double focusing mass spectrometer allows spectra with a unique information content to be generated. The system performance is discussed and several types of spectra are displayed. This abstract will present the information available in each of these spectra separately. (1) Collision-induced dissociation of kiloelectron volt ions gives product ions whose nature and abundance depend on the scattering angle. Increasing angle corresponds to depositing increased internal energy. This is demonstrated by the increased relative abundances of ions formed by multistep versus one-step fragmentation sequences. Angle-resolved data for numerous ions were recorded, these data closely parallel the breakdown curves of the ions in question. (2) Energy-loss spectra and mass spectra of ions which survive strong collisions are recorded. These latter species are typically the lower-mass even electron ions which are least susceptible to charge exchange. These spectra represent the stability of the various ions present in the mass spectrum with respect to their depletion via a number of inelastic channels. (3) The phenomenon of fragmentation from isolated electronic states should be recognizable from the angle-resolved data. The occurrence of such processes in organic ions has been the subject of continued debate. The data for CS(,2)('+(.)) (Chapter 4.4.4) suggests that ion dissociation is occurring from several states. (4) Variation of the impact energy (E) in conjunction with the laboratory scattering angle ((theta)) at which scattered ions are observed allows control of energy deposition in ion/neutral collisions. This was determined from measurements obtained on the methanol molecular ion. The data set covers an ion kinetic energy range of 750-8000 eV and a range of laboratory scattering angles of 0.1 to 1.5(DEGREES). (5) The effectiveness of different targets in collisional activation was determined by angle-resolved mass spectrometry. Effects of target chemical properties upon ion excitation are small; target mass is the dominant factor controlling excitation for an arbitrary, fixed scattering angle. Light target gases are more effective in energy deposition under fixed experimental conditions; however, heavier targets are intrinsically more effective in the center-of-mass system. The effect of the target nature as it pertains to collision-induced dissociation was investigated. The relative importance of ion removal by scattering out of the collection angle of the detector, as opposed to removal by neutralization, was determined. The loss of ion beam by scattering showed an approximate correlation with the mass of the target. Cross sections for neutralization by charge exchange showed an excellent inverse linear correlation to the ionization energy of the target. In addition, the optimum conditions for collision-induced dissociation and charge exchange were investigated. Energy partitioning in unimolecular dissociations were investigated, and kinetic energy release measurements for C(,6)H(,6)O('+(.)) ions were obtained. In addition, a general instrument-discrimination function was derived.
Degree
Ph.D.
Subject Area
Analytical chemistry
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