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http://hdl.handle.net/1956/2455
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| Title: | Chemical Insights from Carbon 1s Photoelectron Spectroscopy and Theoretical Modeling |
| Authors: | Oltedal, Velaug Myrseth |
| Issue Date: | 31-Aug-2007 |
| Publisher: | The University of Bergen |
| Abstract: | Inner-shell ionization energies provide local probes of the charge distribution
in molecules and of the ability of a molecule to accept charge at specific
sites. As such, core-ionization energies are related to and may provide insight
into other chemical properties that depend on the same ability. X-ray photoelectron
spectroscopy (XPS) is the preferred tool for exploring core-ionization energies.
In the present work, synchrotron radiation was used to acquire photoelectron
spectra of several carbon-containing molecules in the gas phase. Carbon
1s ionization energies are of special interest because of the vital role of organic
molecules in life processes. A prerequisite for obtaining accurate ionization energies
is access to reliable methods for calibration of the energies. This work
has been concerned with establishing procedures for very accurate calibration
of C1s ionization energies.
With today’s instrumentation, it is possible to obtain high-resolution photoelectron
spectra that reveal details of the fine structure which have not been
observed previously. The fine structure may be very complex, due to contributions
associated with the inequivalent carbons in a molecule, as well as vibronic
structure. To assign such a spectrum and obtain chemical shifts, one is dependent
on theory to prepare lineshape models for each carbon in the molecule. In
this thesis, several approaches for modeling vibronic progression in XPS measurements
of hydrocarbons were tested. A relatively simple model for taking
into account effects of vibronic coupling in the spectra was developed. This
model is expected to work well also for larger, more complex systems. With
this tool, it is possible to assign photoelectron spectra and obtain chemical shifts
for the different carbons in a molecule with high accuracy. It is now believed
that vibronic structure arising from core-ionization of hydrocarbons is well understood.
This knowledge has been applied to various molecular systems of
chemical interest. It is shown that core-ionization energies may provide insight
into chemical properties such as proton affinity and reactivity, and how these
properties are influenced by a methyl substituent. Experience from gas-phase
XPS is also found to be of considerable use in assignment of adsorbed-state
photoelectron spectra. |
| URI: | http://hdl.handle.net/1956/2455 |
| ISBN: | 978-82-308-0418-6 (print version) |
| Appears in Collections: | Department of Chemistry
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