Experimental Probes of Gas Phase Ions and Molecules: I. Product Kinetic Energy Release Measurements as a Probe of Reaction Thermochemistry, Dynamics, and Chemical Structure in Systems Containing Transition Metal Ions. II. Photoelectron and Optical Studies of Organic Transient Species

Citation

Dearden, David Vernell (1989) Experimental Probes of Gas Phase Ions and Molecules: I. Product Kinetic Energy Release Measurements as a Probe of Reaction Thermochemistry, Dynamics, and Chemical Structure in Systems Containing Transition Metal Ions. II. Photoelectron and Optical Studies of Organic Transient Species. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/6tyj-gy42. https://resolver.caltech.edu/CaltechETD:etd-02082007-130036

Abstract

The release of kinetic energy in the decomposition of a metastable ion is a reflection of both the overall energetics and the potential energy surface on which the process takes place. Chapter 1 applies measurements of the kinetic energy release distributions (KERDs) for decomposition of metastable Mn(CO)ₓ⁺ to the dynamics and energetics of exchange processes for the CO ligands. All the dissociations can be described by statistical phase space theory, in agreement with efficient CO exchange rates indicating that conservation of electronic spin is not important to the dynamics. A general method is presented and used whereby Mn⁺-CO bond energies are obtained from the KERDs. Chapter 2 deals with reactions of Fe⁺ and Co⁺ with alkanes to eliminate methane, which have KERDs narrower than predicted by statistical theory. Restriction of the angular momentum (or, equivalently, the impact parameter) to values less than those anticipated by simple ion-molecule collision theory can account for the narrowed distributions. The restrictions result from barriers in the effective potential energy surfaces and from limitations in our measurement techniques. In Chapter 3, KERDs are used to demonstrate the existence of cobaltacyclobutane⁺, (hydrido)(cyclopropyl)Co⁺ and Co(propene)⁺ structures which do not interconvert on the µs time scale in the gas phase. Chapter 4 deals with the dehydrogenations of cyclic alkanes by Fe⁺ and Co⁺, and shows that, contrary to previous assumptions, statistical energy partitioning occurs in these processes.

Chapters 5 and 6 deal with studies of transient organic species. Chapter 5 presents preliminary work on charge-reversed, resonance enhanced multiphoton ionization (CRREMPI), a potentially powerful new method which exploits the special characteristics of the ion cyclotron resonance spectrometer to obtain optical spectra of a wide variety of transient species. In Chapter 6 photoelectron spectroscopy is used to observe the rearrangements of primary alkyl radicals, produced by flash vacuum pyrolysis of nitrites, to the thermodynamically more stable secondary isomers. Decomposition processes are also observed.

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