Summary: | This thesis describes the use of density functional theory (DFT) to assist the interpretation of advanced spectroscopic techniques such as stopped flow Fourier transform infrared spectroscopy (FTIR), muon spin resonance (�SR), and nuclear inelastic scattering (NIS). These complementary techniques are used to investigate the structure and mechanism of a variety of important chemical systems, some of which are relevant to biological energy transduction and energy harvesting. The mechanisms by which [FeFe] and [NiFe] hydrogenase enzymes catalyse the reversible reduction of protons to dihydrogen are of intrinsic interest in the context of a developing hydrogen technology for energy transduction. Gas phase DFT calculations are used to simulate and assign structure to experimental solution phase FTIR spectra for a family of [FeFe]-hydrogenase model complexes. Further, the Mulliken charge distribution across the Fe centres are compared for di�erent dithiolate bridge groups and PMe3 ligand positions. In the pursuit of understanding the protonation mechanism of [FeFe]-hydrogenases, transition state theory is used and the energetics of reaction pathways leading to terminal and bridging hydrides calculated and compared. NIS demonstrates great potential for characterising the [FeFe]-hydrogenase mimics. In order to further develop and validate the technique, a combination of NIS, DFT calculations, FTIR and Raman spectroscopies are applied to a small Fe(III) model system in order to provide complete a characterisation of the low frequency metal
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