Soft x-ray spectroscopy of organic and organometallic molecules and polymers
In this thesis, two aspects of research in soft X-ray absorption spectroscopy chemistry are explored. The first objective was to measure the natural circular dichroism of small chiral organic molecules at soft X-ray wavelengths. The second objective was to characterize the electronic structure and spectra of a series of organometallic polymers. The goal of the first part of this thesis was to enhance the sensitivity of Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy to the intrinsic “handedness” of chiral organic molecules. The phenomenon of X-ray natural circular dichroism (XNCD) has been well described by theoreticians; however, there have been few successful measurements reported, mainly due to the weakness of the effect and the difficulty of preparing suitable samples. The fourth chapter of this thesis outlines the requirements for XNCD experiments and the efforts made to prepare appropriate samples. The goal of the second part was to use NEXAFS spectroscopy as an analytical technique for the elemental and chemical characterization of innovative materials based on organoiron compounds. The interpretation of transition metal compounds by NEXAFS spectroscopy is difficult due to complex interactions between the metal and its surroundings. Two approaches are commonly used; an atomic multiplet model and a covalent bonding model, which lead to conflicting spectral assignments. Earlier NEXAFS studies of metallocene complexes were found to be lacking as these two models were not adequately rationalized. Owing in part to greatly improved instrumental sensitivity and to efficient theoretical calculations, the interpretation of NEXAFS spectra for a series of metallocene and metal arene complexes was refined. Enhanced understanding of the spectroscopy of these compounds eventually contributed to the characterization of a series of organometallic polymeric materials.Underlining these studies is the remarkable complementarity of NEXAFS spectroscopy and chemistry. A comprehensive understanding of the chemistry of the samples examined in the measurement of XNCD is shown to be crucial for a successful advancement of this spectroscopy. In return, optimization of soft X-ray spectroscopy of metallocenes is demonstrated to remarkably benefit the understanding of the organometallic polymers.
DegreeDoctor of Philosophy (Ph.D.)
CommitteeMoewes, A.; Kennepohl, P.; Majewski, M.; Baranski, A.; Ward, D.
Copyright DateMarch 2008
x-ray absorption spectroscopy