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

The results of an investigation of the vibrational kinetics of carbon monoxide in a supersonic expansion are presented. In the experiments, arc-heated argon was seeded with CO (5–20%) and expanded to Mach numbers of 4.0 to 4.2. The vibrational state of the gas was determined by obtaining individual vibrational populations from the CO overtone emission spectra. The vibrational distribution at the nozzle exit was observed to be non-Boltzmann, in good quantitative agreement with the anharmonic model of vibrational relaxation.