Date of Award

Spring 1968

Degree Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Chemistry

First Advisor

Ehlert, Thomas C.

Second Advisor

Haworth, Daniel T.

Abstract

Approaches to the study of bond dissociation energies span a broad spectrum from those chiefly concerned with quantum mechanical methods to those developed from electrostatic principles. Using quantum chemical methods, exact solutions for energy terms can only be calculated for molecular systems containing one to six electrons. C .A. Coulson, speaking at the Conference on Molecular Quantum Mechanics in 1959 (1), predicted that these calculations might be extended to yield effectively exact solutions over a range of six to twenty electrons. He warned, however, that an accuracy of this order of , magnitude would be purchased very dearly. An ability then, to calculate bond energies using other than quantum theoretical methods for simple diatomic gaseous molecules is highly desirable. Good experimental data obtained by different techniques, thermochemical as well as spectroscopic, which confirms or illustrates deficiencies in calculated bond energy values are equally necessary. It is the purpose of this study to extend the use of a theoretical electrostatic approach, to modify that approach, and to attempt to determine, using mass spectrometric means, bond energies of calcium and magnesium monohydride. The electrostatic model of a diatomic molecule under study in this thesis is the Rittner Ionic Model which was proposed in 1951. Rittner's Model has been successfully applied to the calculation of bond energies of gaseous diatomic molecules (2,3,4,5), used in reverse calculations to determine spectroscopic molecular constants (6,7,8) and more recently, for the determination of dimerization energies (9) . In this thesis the Ionic Model has been reexamined for the Group IIA monofluorides and monochlorides in the light of newer molecular constants where these were available and has been extended to the calculation of bond energies for the monohydrides, sulfides, and oxides of this same periodic group in an effort to further test the limits of its range of usefulness. After studying the results of these calculations a modification of the polarizability values for the anions in the molecules under study was explored as a method of making the model more widely applicable . Finally a mass spectrometric study of calcium and magnesium monohydrides was carried out. Data from this study were used to estimate their bond energies .

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