Raman Spectroscopy of Conformational Rearrangements at Low Temperatures

This thesis identifies the turning point in chain length, after which alkanes self-solvate into a folded structure instead of an extended stretched conformation. After this turning point, London dispersion forces rearrange isolated n-alkanes into a particular hairpin-structure, whilefor shorter chain lengths, a simple stretched conformation is energetically preferred. This thesis can locate the experimentalturning point for the first timein aninteraction-free manner from measurements of unbranched alkanes at low temperaturesin supersonic jet expansions. It contains a detailed analysis of the vibrational Raman spectra of the chain molecules, which is supported by comprehensive quantum chemical simulations. In this way, the detailed balance between inter-chain attraction and conformational flexibilitycan bequantified. The investigations are complemented by measurements of perfluoroalkanes and similarities and differences between the compounds are discussed. Furthermore, Nils Lüttschwagerdetermines the stiffnesses (elastic moduli) of two of the most common industrial polymers: polyethylene and polytetrafluorethylene. He uses in this thesis a sophisticated extrapolation to calculate this value from quantities of their building blocks, showing thatthe single polymer molecules can be as stiff as a rod of steel.