Photoelectron Spectroscopy of Reactive Intermediates

Citation

Kruppa, Gary Hermann (1988) Photoelectron Spectroscopy of Reactive Intermediates. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/jytn-vs45. https://resolver.caltech.edu/CaltechTHESIS:02202013-105931312

Abstract

Photoelectron Spectroscopy (PES) has been used to investigate the structure and thermochemistry of a number of alkyl radicals and their corresponding carbonium ions. The radicals have been produced by flash vacuum pyrolysis of alkyl nitrites. The shape of the first band in the photoelectron spectrum of a free radical is related to the structural changes that take place in forming the carbonium ion from the radical. The ionization potentials obtained from the photoelectron spectra of the radicals are combined with gas phase ion thermochemistry data to obtain alkyl radical heats of formation. The thermochemical data thus obtained is used to discuss substituent and structural effects on the stability of radicals and carbonium ions. In many cases the thermolytic decomposition pathways of the alkyl radicals have been elucidated using PES. The application of the PES technique to the analysis of reactive intermediates present in heterogeneous thermolysis mixtures is also discussed.

Chapter 1 presents an introduction to the technique employed in these studies, and a review of the studies performed in this laboratory. Chapter 2 presents results on the thermochemistry and structure of the 1- and 2-adamantyl radicals. The tricyclic 1-adamantyl radical and carbonium ion are important as model bridgehead compounds, and the question of the amount of strain energy caused by the non-planarity of the radical and ion center has been of great interest. The first bands in the photoelectron spectra of the o-, m- and p-methylbenzyl radicals are presented in Chapter 3. The methyl substituent effects on the stabilities of the radicals and ions are discussed.

In Chapter 4 results on investigations of heterogeneous processes in Chemical Vapor Deposition (CVD) systems using the chlorosilanes as feed gases are discussed. SiCl₂ is found to be the major silicon containing reactive intermediate produced by surface reactions at 600 - 1100 °C in CVD systems using dichlorosilane and trichlorosilane as feed gases.

Chapter 5 presents the spectra of the 1- and 2-methylnaphthyl radicals. The relative stabilities of the radicals and carbonium ions are discussed based on proton affinities determined by Fourier transform mass spectrometric equilibrium studies, combined with ionization potentials obtained from photoelectron spectra of the radicals.

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