Measurement of vibrational population distributions in a supersonic expansion of carbon monoxides

The results of an investigation of the vibrational kinetics of carbon monoxide in a supersonic expansion are presented. In the experiment, arc-heated argon was seeded with CO (5-20%) and expanded to Mach numbers of 4.0 to 4.2 in a time scale of 50 microsec. The stagnation temperature was varied between 2000K, and 3000K, and the stagnation pressure was approximately 7 atm. (abs). The vibrational state of the gas was determined by spectrally resolving the first overtone vibrational-rotational radiation from the CO, and obtaining individual vibrational populations from the emission spectra. The theoretical model used to describe the vibrational kinetics accounted for the anharmonic vibrational energy level structure of CO. Rate equations were formulated that describe the evolution of the populations of the individual levels due to vibration-translation, vibration-vibration and radiative processes as the gas flows through the nozzle.