This thesis reports the study of the molecular and electronic structure of scandium monohalides using the technique of laser ablation/reaction with supersonic free jet expansion used for producing the target molecules and laser induced fluorescence (LIF) spectroscopy for recording their electronic transition spectrum. The scandium diatomic molecules studied in this work were scandium monoiodide (ScI) and scandium monobromide (ScBr), which were produced by the reaction of Sc atoms with 2% CH3I and 2% C2H5Br gases seeded in Ar carrier gas, respectively. The LIF spectrum of the electronic transition of ScI and ScBr were recorded in the visible and near infrared spectral region between 613 and 854 nm. The analysis of the high resolution electronic spectra of ScI and ScBr yielded molecular constants and information of electronic structures. For all the transition bands observed, rotationally-resolved transition lines were fit to a theoretical model to retrieve molecular constants for both upper and lower electronic states. For the ScI molecule, seven vibrational bands of the D1П –X^1 Σ^+ system were recorded and analyzed. Accurate molecular constants for the v = 0 – 2 levels of the D^1П state and the v = 0 – 3 levels of the X^1 Σ^+ state were obtained. The equilibrium bond lengths, re (Å), for the electronic states of ScI were determined as follows: ScI X^1 Σ^+ D^1П r_e(Å) 2.6078 2.7146 For the ScBr molecule, three electronic transition systems were recorded and analyzed, which include six vibrational bands of the C^1 Σ^+– X^1 Σ^+ system, seven vibrational bands of the e^3Δ–a^3Δsystem and two vibrational bands of the d3Φ – a3Δ system. Rotationally resolved transition lines of both Sc79Br and Sc81Br isotopes were observed and analyzed. Least-squares fitting of the measured line positions yielded accurate molecular constants for the v = 0 – 2 levels of the X^1 Σ^+ state, the v = 0 – 3 levels of the C^1 Σ^+ state, the v = 0 and 1 levels of the d3Φ state and the v = 0 – 2 levels of both e3Δ and a3Δ states, respectively. The equilibrium bond lengths, re (Å), determined for electronic states of ScBr are given as follows: ScBr X^1 Σ^+ a^3Δ C^1 Σ^+ r_e(Å) 2.3806 2.4767 2.4776 A molecular orbital (MO) energy level diagram has been used to examine the electronic configurations giving rise to the different observed electronic states of ScI and ScBr. An attempt has been made to put the MOs of all the scandium monohalides under a single picture. A comparison of the molecular constants for the different electronic states of scandium monohalides indicates a weakening of the chemical bonding between the scandium atom and the halogen atoms down the group. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / toc / Chemistry / Master / Master of Philosophy

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Metal trihalide (MX₃) systems represent a stern challenge in terms of constructing transferable potential models. Starting from a previously published set of potentials, 'extended' ionic models are developed which, at the outset, include only anion polarization. Deficiencies in these models, particularly for smaller (highly polarizing) cations, are shown to be significant. For example, crystal structures different to those observed experimentally are adopted. The potentials are improved upon by reference to ab initio information available for alkali halides with the 'constraint' that the parameters transfer systematically in a physically transparent manner, for example, in terms of ion radii. The possible influence of anion compression ('breathing') and the relative abundance of anion-anion interactions are considered. Simulation techniques are developed to allow for the effective simulation of any system symmetry and for the study of transitions between different crystals (constant stress). The developed models are fully tested for a large range of metal trichloride (MCl₃) systems. Particular attention is paid to the comparison with recent neutron and X-ray diffraction data on the liquid state. Polarization effects are shown to be vital in reproducing strong experimental features. The excellent agreement between simulation and experiment allows for differences in experimental procedures to be highlighted. The transferability is further tested by modelling mixtures of the lanthanides with alkali halides with potentials unchanged from the pure systems. The complex evolution of the melt structure is highlighted as the concentration of MCl₃ increases. The effectiveness of the models is tested by reference to dynamical properties. Particular attention is paid to the comparison with Raman scattering data available for a wide range of systems and mixture concentrations. The simulated spectra are generated both by a simple molecular picture of the underlying vibrations and by a more complex (fluctuating polarizability) model in which the spectra are broken down into contributions from different mechanisms. This comparison allows for the validity of treating network-like systems as a series of 'isolated' molecules to be assessed. The transferability of the potentials is pushed to the limits by modelling metal tribromides, in which the parameters are obtained from the trichlorides by the same simple scaling arguments.

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Thesis (Ph.D.)--Dept. of Physical and Inorganic Chemistry, University of Adelaide, 1973. / "September 1973." Includes bibliographical references.

Thesis (M.Sc.) -- University of Adelaide, Dept. of Organic Chemistry, 1975.