Experimental Investigation of Carbon Dioxide Jet Plumes

Free jets, produced by issuing ${\mathrm{CO}}_2$ gas from a supersonic nozzle into high vacuum, have been investigated experimentally by measuring densities and temperatures of the gas. Gas densities are measured using electron beam absorption and luminescence methods. Rotational temperatures are measured, after a theoretical model is developed, by using an unresolved band system of the ${\mathrm{CO}}_2$ spectrum. The results indicate that condensation must take place inside the nozzle. Outside the nozzle, the expanding gas gradually leaves the saturation line. At a pressure of about 0.3 Torr the condensation is frozen, and beyond this point the gas essentially follows an isentropic expansion line.