Thomas, L.H.; (2007) Computational quantum chemical studies of main group and transition metal molecules and ions. Doctoral thesis , University of London.

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Abstract

This thesis describes three computational studies the decomposition of BCl, the geometric and electronic structures of ferrocene and iron pentacarbonvl. and the electronic structure and spectra of the complexes Th(//8C8H8)2. Pa( /8C8H8)2. Th(//8Ch(CH.,).,H.,), and Pa(C8(CH,),H,)2- The prediction and rationalisation of the decomposition products of BCl has been achieved by a characterisation of the lowest energy singlet and triplet potential energy surfaces using ab initio methods. The <% diagnostic has been used to assess the degree of multiconfigurational character in the coupled-cluster wavefunctions. The suitability of this method is determined by a partial re characterisation of the system using multiconfigurational methods. The frag mentation products located are in good agreement with available experimental data provided by mass spectrometry. The structures of ferrocene and iron pentacarbonyl are calculated using a va riety of methods including coupled-cluster (CC) theory. CC from a Hartree-Fock reference produces good structures, but with 2 diagnostics that suggest single reference methods to be unreliable. CC from Kohn-Sham (KS) references return equally good structures, but with significantly reduced & values, suggesting that the f7 may not be a reliable indicator of multiconfigurational character in these systems. The single configurational nature of Fe(CO)s is confirmed by multicon- figurational calculations. Experimentally, Fc(CO)s is observed to have equatorial M-C bonds that are shorter than the axial although the predicted structures agree well with experiment, this feature cannot be reproduced. TD-DFT is used to calculate excitation spectra for thorocene, protactinoceiie and their methyl-substituted derivatives. The experimental UV-vis data for these species are extremely limited and previous theoretical studies give assignments of these data which are not consistent. The effects of the molecular structure and use of different exchange-correlation potentials on the spectrum are investigated for thorocene. Consistent excitation spectra for each species are calculated and assigned these are used to suggest new assignments of the experimental data.

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