This work studies the collisional excitation kinetics of atomic oxygen diluted in argon at extreme temperatures (8,000 - 11,000 K) in a shock tube. Two lasers at 777 and 926 nm were scanned across the transitions of atomic oxygen at a rate of 25 kHz, providing the absorbance time histories within the 0.5-1 ms test time after the reflected shock passed. Four key quantities were measured in the current work to understand the collisional excitation kinetics, namely, the number density of the: fourth level of atomic oxygen; sixth level of atomic oxygen; electrons; and heavy-particle translational temperature. The number density of atomic oxygen and heavy-particle translational temperature were inferred from the integrated area and the Doppler linewidth of the measured oxygen absorbance. A preliminary two-temperature collisional-radiative model was developed to explain the multi-stage behavior of the measured oxygen number density time histories from 8,000 to 10,000 K. Reaction rate constants were fitted to match the measured excited-state atomic oxygen time histories. A sensitive, in-situ electron number density diagnostic method was developed by measuring the Stark shift of excited-state atomic oxygen. The measured electron number density was consistent with the preliminary model. The kinetics model was revised to match the measured time histories from 10,000 to 11,000 K.

The laser Raman scattering technique shows potential as a diagnostic method for determining the chemical and thermodynamic state of high-temperature gases. To investigate the utility of this technique for shock-tube diagnostics, and to validate the method at known elevated temperatures, vibrational Raman intensities were measured behind an incident shock wave. Intensity history data through the wave front, vibrational excitation times of oxygen in air, along with temperature and density measurements for oxygen and nitrogen in air were obtained over a range of postshock conditions. The measured densities and temperatures were found to be in good agreement with shock-wave theory. An excitation time measurement also agreed well with shock-tube data obtained with other diagnostic methods. In general, the results indicated that the Raman scattering technique was accurate at elevated temperatures and should prove useful in determining the thermochemical state of gases in continuous flows as well as in shock tubes and other impulse facilities.

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