On parallel and sequential dissociations in energy selected ions
Public Deposited- Last Modified
- March 21, 2019
- Creator
-
Kercher, James P.
- Affiliation: College of Arts and Sciences, Department of Chemistry
- Abstract
- The ability to extract rate constants and dissociation energies of parallel and sequential dissociation pathways in energy selected ions has been made possible by recent advances in threshold photoelectron photoion coincidence (TPEPICO) spectrometry. The incorporation of velocity focusing optics for improved instrument resolution, the ability to subtract the energetic electron contamination in the threshold signal and a more robust modeling program are the key components in allowing higher energy reactions to be probed. In addition, the recent advances in computational chemistry have allowed the experimental results to be supported quickly and accurately. In many cases it has been used to uncover reaction mechanisms that would otherwise remain hidden. The work in this thesis is devoted to obtaining kinetic and thermochemical information from higher energy dissociation pathways. Both parallel and sequential reactions are discussed. The broad range molecules for which this technique can be applied makes it both useful and attractive. Chapter 1 is an introduction to the work presented, dealing with the motivation and methods of obtaining thermochemical properties of molecules. Chapter 2 is the description of the experimental and theoretical methods which are applied. A temperature dependant study on the iodine loss in n-butyl iodide ions is described in Chapter 3. Modeling this single-step reaction only requires the thermal energy distribution, but it provides a useful place to start, since the first step in parallel and sequential reactions are treated in the same manner. Chapters 4 and 5 deal with the determination of the physical properties of the acetyl ion and radical and well as the propionyl ion and radical from parallel dissociations of several energy-selected ketone ions. The thermochemsitry of six dihalomethanes of the form CH2XY, where X and Y are any combination of Cl, Br, and I are discussed in Chapter 6. In this analysis of parallel reactions, a complete thermochemical cycle is established to ensure that the results are self-consistent. Chapter 7 deals with the sequential ethane loss channels in a series of energy-selected ethyl phosphine ions. The statistical theory of energy-partitioning is used to extract dissociation onsets. Chapeter 8 is a study on 2-pentanone, an ion very similar to those studied in chapters 3 and 4, but one that dissociates in a much more interesting and complex manner. Although only 3 fragment ions are observed in the TOF distribution, there are 4 parallel and 1 sequential dissociation pathway. The ability to model these reactions clearly illustrates the power of the TPEPICO technique.
- Date of publication
- December 2006
- DOI
- Resource type
- Rights statement
- In Copyright
- Advisor
- Baer, Tomas
- Language
- Access right
- Open access
- Date uploaded
- October 19, 2010
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