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Theory of molecular auger spectroscopy

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Chelkowska, Elzbieta Zofia (1993) Theory of molecular auger spectroscopy. PhD thesis, University of Tasmania.

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Abstract

Auger electron spectra of molecules are in general more complex than the spectra of the
isolated constituent atoms because the increased number of valence electrons in molecules
results in a significantly larger number of final double-hole states. Ab initio calculations are
possible but their complexity restricts optimized studies to a limited number of relatively
small molecules.
Alternative approaches are sought to simplify calculations. Semi-empirical methods are
very promising since the results are often at least of the same level of accuracy as minimum
basis ab initio calculations, yet the answer is obtained within a small fraction of effort
required for ab initio computations.
In this work a semi-empirical method developed for atomic problems and adapted for
molecules by Larkins is extended and appraised. All molecular Auger calculations are
performed at the INDO or STO-3G level.
In the present approach the intensities of molecular Auger transitions are calculated using
the intra-atomic model presented by Siegbahn. The exact expressions for intensity
calculations depend upon the symmetry of the orbitals involved while the complexity of the
calculations increases with the size of the basis set. For calculations within this project using
first- or second-row atoms the smallest basis set sp is considered sufficient.
Molecular Auger energies are calculated as the difference in the experimental binding
energies of the core and valence molecular orbitals involved in transitions corrected by a
term which includes the hole-hole interaction energy. The correction term depends on the
symmetry of the final double-hole state and is calculated as a simple function of Coulomband
exchange-type integrals. Using the above approach some KVV and LVV Auger spectra of molecules containing first and
second-row elements are calculated. In particular, the method is applied to interpret the
KVV and LVV spectra of the first- and second-row hydrides respectively. Moreover,
theoretical and experimental spectra of CH3-X (where X=F, OH, NH2, CH3) are compared
when the influence of the chemical environment on the carbon KVV Auger transitions is
investigated. The theoretical results are in satisfactory agreement with the experiment. In
addition, the theory is tested by comparison with the experimental spectra of the first- and
second-row tetrafluorides. There are some discrepancies between theory and experiment for
highly symmetric molecules. On the basis of undertaken calculations C(KVV) molecular Auger spectra of XCHO (where
X=F, OH, NH2, CH3) are predicted. The theory is also verified for an example of secondrow
polyatomic molecule - OCS. The intensity calculations of the molecular S(LVV) Auger
spectrum are the first direct evaluation based upon the molecular wavefunction for this type
of molecules. The calculations can be extended to the compounds containing the third row
elements.
The overall agreement between theory and experiment is most encouraging nevertheless
absolute energy calculation requires some minor refinement. It is concluded that this
method represents an efficient approach for the interpretation of complex Auger spectra
and may be extended to larger polyatomic systems with d orbitals.

Item Type: Thesis (PhD)
Keywords: Auger effect
Copyright Holders: The Author
Copyright Information:

Copyright 1993 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1994. Includes bibliographical references

Date Deposited: 25 Nov 2014 00:42
Last Modified: 19 Jul 2016 01:59
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