Michael McCann

Publication Date

11-1980

Advisor(s) - Committee Chair

James Parks, Earl Pearson, Curtis Wilkins

Comments

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Degree Program

Department of Chemistry

Degree Type

Master of Science

Abstract

Resonance Ionization Spectroscopy is a sensitive analytical technique capable of detecting a single atom in a background of 1019. Resonance Ionization Spectroscopy, as applied in this experiment, employs two lasers in coaxial geometry. An ultraviolet laser is used to photodissociate cesium iodide. The neutral cesium atoms are generated between two parallel plates in a cell that is filled with argon. A visible laser ionizes the cesium, and the electrons are detected in a parallel plate ionization chamber.

The ultraviolet laser photodissociates the cesium iodide molecules into neutral fragments. The cesium atoms are created in a very well defined volume and at a known time. The neutral cesium is photoionized through a resonance ionization spectroscopy (RIS) scheme with the visible laser. The fluence of the visible laser at the focus is more than sufficient to ionize all the cesium atoms within the defined volume. The defined volume is determined by the cross sectional area of the visible laser beam as it passes through the parallel plates. Ionization occurs in an argon atmosphere between two oppositely biased parallel plates.

Both the ultraviolet and the visible lasers are pulsed. The cesium atoms are generated at a specific time. At a later and predetermined time, the visible laser is fired. Then the cesium atoms are photoionized, and the resulting electrons detected by the parallel plate detector. By changing the delay between the firing of the two lasers, the concentration of cesium atoms within the defined volume can be resolved with time. Factors that affect the concentration of cesium in the defined volume are diffusion and reaction of the cesium with other atoms or molecules. Diffusion out of the defined volume prevents the cesium from interacting with the visible laser and therefore from being ionized. Any cesium in the dfined volume that reacts with other atoms or molecules will not be ionized because the visible laser is tuned to ionize only neutral cesium atoms. Cesium compounds, because of the change in electronic structure, will be ionized at wavelengths different from the wavelength of the visible laser.

By plotting the cesium signal versus the delay time between the two lasers, diffusion coefficient and the reaction rate can be determined. The purpose of this experiment was to determine the reaction rate of cesium with oxygen. Factors affecting the reaction rate such as oxygen pressure, argon pressure, and temperature are examined also.

The reaction rate equation for cesium and oxygen was found to be to the 0.96±.02 order with respect to oxygen. The rate coefficient is (2.3±.2)x10-30sec-1 particle-2cm6. This rate was calculated using the temperature of the chemical cell exterior which was 32°C.

Disciplines

Chemistry | Physical Sciences and Mathematics

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