M.Sc. (Chemistry) / The storage as solid Ag12BI(s) of reactor produced 12BI (t~ = 1.6 x 107 a) in underground respositories can present an environmental problem due to the potential release of radioactive 12BI into the environment over extended storage periods. One process that causes concern is the solubilization of AgI through complexation when brought into contact with underground water, particularly those with high salt content. In this work the charaqterization of the complexation equilibria in the AgI(s)/I-(aq),CI-(aq) system was studied. Solu- I tions containing high CI- and low 1- concentrations were of special interest with regard to the possible formation of ternary complexes. The presence of AgICI22- was indicated experimentally but no evidence of other ternary species like AgI2CI2- or AgIsCIS- could be established. Solubilities were determined radiochemically by using specially prepared 110mAgI. Solubility curves for AgI in different I-/CI- mixtures were adequately explained in terms of models consisting of the species AgCls2-, AgC14S-, AgIs2-, AgI4s- and AgICI22-. Distribution curves were calculated for different I-/CI- mixtures. As an alternative detection mode for silver-determination a flow injection system incorporating a micro-column of activated alumina was used in conjuntion with flame atomic absorption spectrometry for the pre-concentration and determination of silver in water. The procedure was successfully applied to a range of water samples, but no determination of silver in halide or perchlorate media was possible. The limit of detection based on a sample volume of 15 cms was 4.5 ~gdm-3 and the relative standard deviations at 50 and 5 ~gdm-3 were 5.4 and 19%, respectively. In part B of this work a method for the determination of chloride in organic compounds (oils provided by the Atomic Energy Corporation) by using an Parr oxygen bomb and ion chromatography was studied. The combustion products were absorbed in H20. The solution was injected into an ion chromatograph equipped with an anion analytical column, membrane suppressor and conductivity detector. The instrument response was calibrated using different standard solutions. These were prepared from several organic solutions, an organic salt and from sodiumchloride. Calibration curves were linear over a wide range and presented good reproducibility. It differed however according to the type of standard solution used. The limit of detection was 255 ~gdm-3 and the relative standard deviations at 10, 1 and 0.5 ugcm-3 were 0.52, 1.64 and 3.5%, respectively. As an alternative decomposition method wet decomposition within a sealed system (autoclave) was used. Due to the high blank values in this method no analysis of substances could be made in the lower ugcm-3 range.

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The investigation presented here is in two parts: a mechanistic study of the triethylamine dehydrohalogenation of ac-haloacid halides to form halogenated ketenes and a study of steric influence upon ketene lifetimes. The first part of this research deals with the mechanism of the dehydrohalogenation reaction. Two acid halides, isobutyryl chloride and a-chloropropionyl chloride, appeared to represent two mechanistic extremes for this reaction with triethylamine. Isobutyryl chloride reacted with triethylamine to form an acylammonium salt while a-chloropropionyl chloride produced the enolate salt. These salts were detected in chloroform solution by both nuclear magnetic resonance spectra and infrared spectra. The results of the investigation into the mechanism of dehydrohalogenation and ketene lifetime were complemented by CNDO/2 calculations of the acid halides and ketenes studied. It was concluded that the mechanism of dehydrohalogenation of acid halides involves a complex series of equilibria,and it has become increasingly apparent that halogenated ketenes are produced through the acylammonium salt. The enolate salt appears to be a dead end in the reaction to form ketenes. It was also demonstrated that increasing steric bulk has a stabilizing effect on ketene lifetimes.

No description available.

No description available.

published_or_final_version / Radio Chemistry / Master / Master of Science

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The thesis is concerned with the derivation of anisotropic intermolecular potentials from experimental data. For the rare gas - hydrogen halide systems the most useful experimental results are those from molecular beam rotational spectra of van der Waals complexes and from pressure broadening of hydrogen halide rotational spectra by rare gases. Intermolecular potentials for the Ar.HCl system had previously been obtained from each of these experiments separately, but none of the potentials proposed succeeded in reproducing all the available data. In the present work, improved theoretical methods are developed for the calculation of molecular beam spectra and line broadening cross sections from a proposed intermolecular potential. The methods developed are substantially faster than those previously available, allowing their use in a least squares procedure to determine potential parameters. Several possible parameterisations of the intermolecular potential are then considered for Ar.HCl, and least squares fits of potential parameters to experimental results are performed for this system. Measurements of total differential cross sections and second virial coefficients are included in the least squares fits, in addition to the experiments mentioned above. The experimental data demonstrate conclusively that the equilibrium geometry of Ar.HCl is linear, with the atomic arrangement as written. The equilibrium intermolecular distance is 400±3 pm, with an absolute well depth of 18andpm;10 cm^-1 . The only feature of the potential which is not well determined by the experimental results is the behaviour around the linear Ar.Cl-H geometry. The results for Ar.HCl are then extended to the systems Ne.HCl, Kr.HCl and Xe.HCl, allowing the dependence of the intermolecular potential on the rare gas to be considered. The molecular beam spectra for Ne.HCl can be fitted only by a potential with a secondary minimum at the linear Ne.Cl-H geometry, in addition to the primary minimum at the linear Ne.H-Cl geometry. The experimental results for the other rare gas - HC1 systems are not very sensitive to this feature of the potential, and the potentials for these are constrained to be similar to that for Ne.HCl in this region. The potential surfaces for all the rare gas - HC1 systems have similar shapes, and appear to be nearly conformal. Finally, intermolecular potentials are obtained for the systems Ar.HF, Kr.HF and Xe.HF from molecular beam spectra. The experimental data for these systems are less extensive than for the HC1 systems, and the potentials obtained are reliable only in the region of the absolute minimum. The HF systems are considerably more anisotropic than the HC1 systems, and it is suggested that this is principally due to greater induction forces in the HF systems. Experiments are suggested which would provide further information on the intermolecular potentials for both HF and HC1 systems, and predictions of the results are made using the current best fit potentials.

Thesis--M. Sc., University of Hong Kong. / Typewritten.