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This thesis presents theoretical investigations that elucidate experimental observations and test theory.\ud Firstly, density functional theory (DFT) is used to determine the mechanism for Pd(0) formation from the pincer palladacycle, PdSCN, with and without solvent effects. The elucidated mechanism involves two key steps, transmetallation and reductive elimination. Transmetallation is computed as the rate-determining step and the energy barriers to increase with increasing solvent dielectric constant.\ud The thermal Claus process is an industrially important method of liquid sulfur production from H2S, yet there remain questions of why liquid sulfur is paramagnetic and why H2S persists in recovered sulfur. To answer these questions, a suitable computational methodology is established and used to investigate the structure and stabilities of cyclic and open chain Sn (n ≤ 5 and 8) on the singlet and triplet potential energy surfaces (PESs). All stable cyclic structures are found to have singlet states whereas open chain structures, S, S2, S5 and S8 have triplet ground states. These results provide a possible explanation for the observed paramagnetism of liquid sulfur. The mechanism for formation of hydrogen polysulfanes (HSn+1H) from open chain Sn and singlet H2S is thereafter investigated. In all cases the most stable HSn+1H is formed exergonically on the singlet PES. However, in the case of Sn clusters with a triplet ground state, the singlet product arises from curve crossing and the triplet product is formed endergonically. The instability of the triplet product provides a mechanism for the persistence of H2S.\ud The DFT correlation functional, LYP, is based on a correlation energy formula derived from the Hartree-Fock (HF) second order reduced density matrix and an exponential correlation factor obtained by fitting to helium data. In this thesis, the formula is re-parametrised using accurate HF densities for helium and hydride and the correlation energy calculated for several atomic systems. |
