Title

The chemistry of meteoric metals in the upper atmosphere

Date of Award

1991

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Marine and Atmospheric Chemistry

First Committee Member

John Plane, Committee Chair

Abstract

The metals Na, Li, K, Ca and Fe have been observed around 90 km in the earth's upper atmosphere. Meteoric ablation is believed to be the source of these metals. The mesospheric chemistry of these metals and their impact on the general chemistry of the atmosphere are poorly understood. Therefore, a detailed investigation of processes affecting the gas-phase chemistry of these metals was undertaken.Both kinetic and photochemical studies were carried out using the techniques of pulsed photolysis of a suitable metal precursor and laser induced fluorescence of the resulting metal atoms. Ab initio calculations were also carried out to study the geometries of the metallic species and calculate their thermochemical properties.Kinetic investigations on the recombination reactions of the alkali metals with O$\sb2$ were performed over an extended temperature range (230-1100 K) in an attempt to understand their different seasonal behavior. The three reactions have very similar temperature dependences over the experimental temperature range. Use of the Troe formalism indicates that this dependency will continue into the mesospheric temperature range (140-240 K). The similarity suggests that differences in the temperature dependence of these reactions are not responsible for the different seasonal behavior of the alkali metals.The lower limits for the bond energies of the alkali superoxides were estimated from the kinetic decays obtained at 1100 K, and then combined with ab initio calculations to yield recommended bond energies. These values are of use in the Troe formalism and the mesospheric models.To assess the effectiveness of NaO$\sb2$ as a daytime sink, the absolute cross-section for photodissociation of NaO$\sb2$ was measured at 230 K. The photolysis rate of NaO$\sb2$ was derived above 70 km. The results indicate that above 85 km the reaction between NaO$\sb2$ and O is a more important loss term for NaO$\sb2$ than daytime photolysis and that between 80 and 65 km the photolysis of NaO$\sb2$ is the dominant loss term. From the photolysis experiment, an atmospherically important new Na species, NaO$\sb4,$ was identified.The bimolecular reactions of Na with HCl/DCl, N$\sb2$O, and Li with H$\sb2$O were investigated. The possible role of the reaction between NaCl and H in the chlorine catalyzed destruction of O$\sb3$ was explored.Finally, the role of the reactions of dissociative electron attachment to NaHCO$\sb3$ and NaCO$\sb3$ in the formation of sudden sodium layers above 90 km was examined by ab initio and thermochemical calculations. The results indicate that NaHCO$\sb3,$ an unreactive species in the mesosphere, can result in the formation of SSLs on collision with energetic auroral electrons.

Keywords

Chemistry, Physical; Physics, Atmospheric Science; Environmental Sciences

Link to Full Text

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