Masters Theses

Date of Award

8-1993

Degree Type

Thesis

Degree Name

Master of Science

Major

Physics

Major Professor

James W. L. Lewis

Committee Members

Crater, Mason

Abstract

Laser-induced fluorescence is a common method for investigating the spectra of gases in flames. The spectra obtained is highly dependent upon the wavelength of the exciting laser line, the pressure and temperature of the flame, and the molecular species in the flame. Such spectra may be compared to theoretical predictions of the spectra to estimate the flame temperature. However, several factors can introduce considerable error in such estimates. Of primary concern in this thesis is the influence of collisional quenching effects upon the number densities of various states of the hydroxyl radical, OH. Two types of calculations have been done to investigate the influence of quenching upon temperature estimates. One method involves taking ratios of spectral lines over a range of temperatures. For two rotational transitions, this ratio cancels out the quenching terms, leaving a ratio dependent only on temperature, term values and line strengths. I have modified this technique to take ratios of two regions of intensities. Quenching will not cancel in this case, but the ratio may provide a good approximation to temperature for cases where the experimental spectra are too broad to single out individual rotational lines. The second calculation involves a set of rate equations which correspond to number densities of various levels involved in the excitation/deexcitation process in LIF. Various models are used to estimate number densities of various vibrational and rotational states. This information may be used to supplement the ratio method in determining the flame temperature.

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