Title

The gas-phase oxidation reactions of alkali and alkaline earth metal atoms

Date of Award

1993

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

John M. C. Plane, Committee Chair

Abstract

The purpose of this kinetic study is to understand the non-Arrhenius behavior for the bimolecular reactions of Group 1 and 2 metal atoms and N$\sb2$O and the temperature dependencies of the termolecular reactions of Group 2 metal atoms and O$\sb2$. Group 1 and 2 atoms were produced in an excess of N$\sb2$O or O$\sb2$ with bath gases, N$\sb2$ or He, by the pulsed photon (193.3 nm) dissociation of metal halides and then monitored by time-resolved laser-induced fluorescence spectroscopy at a specific wavelength. There are clear upward curvatures in the Arrhenius plots for the reactions K + N$\sb2$O and Ca + N$\sb2$O, and the best descriptions of the temperature dependence of the rate constants over the experimental ranges are given in chapters 3 and 4. Theoretical calculations of the reaction of Li and N$\sb2$O demonstrate that the multi-path reaction channel involves bending and antisymmetric vibrational modes in the reaction system. Furthermore, several models including the transition-state theory, dual-path model, Fontijn-Futerko model and the model of vibrational excitation of N$\sb2$O were employed to discuss Group 1 and 2 reactions with N$\sb2$O.A significant difference in kinetic behavior exists between the Group 1 and 2 atom reactions with O$\sb2$. The recombination reactions of Group 1 metals with O$\sb2$ to form superoxides are characterized by large rate coefficients with small negative temperature dependencies, whereas the analogous reactions of Mg and Ca exhibit complex temperature dependence. The Mg reaction is extremely slow. Theoretical study of the geometries of MgO$\sb2$ and CaO$\sb2$ shows that they have different structures in the recombination reactions.A study of chemiluminescence of CaO shows that the strong orange emission exists between 590 and 630 nm, with a lifetime of 27.8 $\pm$ 1.2 ns, and emission beyond 760 nm with a lifetime of 149 $\pm$ 11 ns. The former emission is assigned to the orange arc bands of CaO, and the latter to the CaO(A$\sp1\Sigma\sp+ -$ X$\sp1\Sigma\sp+$, $\Delta\nu <$ 3) bands. Evidence is presented which suggests that the precursor may be the CaO dimer.

Keywords

Chemistry, Physical

Link to Full Text

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