Modeling of complex ionic dissociation reactions observed by TPEPICO spectroscopy

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  • March 21, 2019
Creator
  • Stevens, William R.
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • TPEPICO spectra of dissociatively ionized chlorobenzene, bromobenzene, and iodobenzene have been measured to test the ability of different statistical rate theories to accurately calculate rate constants of homolytic bond cleavages of ions. For this purpose we have developed a method for extracting experimental rate constants at a single internal energy from TPEPICO spectra of thermal ions. It was determined that, of the theories tested, simplified versions of variational transition state theory (VTST) and statistical adiabatic channel model (SACM) were both capable of fitting the rate constants and predicting the known bond energies of all three halobenzenes. RRKM theory was capable of fitting the rate constants but predicted a bond energy that was too low. PST could neither fit the data nor predict the correct E0. The much simpler to employ simplified SACM (SSACM) was applied in the dissociations of nitrosobenzene and neopentane. Chapter 1 is an introduction to the following chapters, dealing with the motivation to determine high precision bond energies of complex dissociations. Chapter 2 is a discussion of the experimental methods employed to observe photoionization and photodissociation processes. Chapter 3 describes the study of the simple isopropyl halide dissociation to determine the isopropyl ion heat of formation. In Chapter 4 we discuss the measurement of rate constants at specific ion internal energies for the dissociation of the halobenzenes in order to compare the ability of different rate theories to model homolytic bond cleavages. Chapters 5 and 6 are applications of the SSACM described in Chapter 4 to the dissociations of the nitrosobenzene and neopentane ions. Like the halobenzenes in chapter 4, the nitrosobenzene ion dissociation is slow and requires rate theories to determine the bond energy. The thermochemistry of the dissociation of both ionic and neutral dissociations of nitrosobenzene are improved using active thermochemical tables. In chapter 6 the bond energy for the methyl loss of neopentane is determined. Although this reaction occurs rapidly, there is a lower energy dissociation pathway that masks the methyl loss channel at threshold thus requiring extrapolation to determine the bond energy.
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  • In Copyright
Advisor
  • Baer, Tomas
Degree granting institution
  • University of North Carolina at Chapel Hill
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  • Open access
Date uploaded
  • October 11, 2010

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