Delocalization and functional group fingerprinting in the core excitation spectroscopy of molecules and polymers

Abstract

<p>Core excitation spectroscopy is a sensitive probe of the local geometric and electronic structure of materials. Functional group "fingerprints" arise in core excitation spectroscopy from a balance between local structural sensitivity and electronic delocalization. Delocalization can add complexity and extended-structure sensitivity to core excitation spectroscopy. In this thesis, Inner Shell Electron Energy Loss Spectroscopy (ISEELS) was used to acquire core excitation spectra of molecules that are structural analogues to polymers, and both ISEELS and Near Edge X-ray Absorption Fine Structure (NEXAFS) was used to acquire core excitation spectra of organosilane molecules. Core excitation spectra of structural analogues of polyurethane, polyurea and polyphthalate polymers were used to model and interpret the spectra of polymers. "Finger-printing" of polymer-relevant functional groups and the sensitivity to polyphthalate substitutional isomerism is demonstrated. Functional group fingerprinting is extended to organosilane molecules for the identification of bond-specific features and electronic delocalization. Molecular orbital calculations were performed to assist spectral interpretation and to examine structure-spectral relationships. Developments in X-ray and electron spectromicroscopy techniques have improved the capability of core excitation for the chemical microanalysis of polymers. In spectromicroscopy of "real-world" materials, the core excitation spectra of these materials must be well understood for meaningful chemical analysis. This thesis provides some of the fundamental underpinnings for the application of core excitation spectroscopy to spatially resolved chemical analysis of organic and organosilane polymers</p>