The primary objective of this study is to advance the development of a procedure for predicting the terminal vibrational temperatures in free−jet flows of either pure gases or gas mixtures. A secondary objective is to apply this procedure to free−jet flows of (a) pure CO2 and (b) dilute binary mixtures of CO2 in N2 and CO2 in H2. Predictions are based on the sudden−freeze model described by Knuth [Proceedings of the 1972 Heat Transfer and Fluid Mechanics Institute (Stanford U. P., Stanford, California, 1972)]. The pressure and temperature dependence of the vibrational relaxation time, required for application of Knuth’s freezing−point criterion, are deduced from available experimental data on relative probabilities for collisional de−excitation of a given species by impurity molecules. The predicted terminal vibrational temperatures are correlated to excellent approximation by a dimensionless scaling parameter based on source conditions. Measurements were made using the supersonic−molecular−beam technique suggested by Milne et al. [J. Chem. Phys. 56, 3007 (1972)]. This technique takes advantage of the temperature dependence of the fragmentation pattern realized when molecules are ionized by electron impact, which temperature dependence can be established quantitatively using an effusive molecular beam with a variable−temperature source. Good agreement between predicted and measured

Sharma, P. K., Young, W. S., Rodgers, W. E., & Knuth, E. L. (1975). Freezing of vibrational degrees of freedom in free-jet flows with application to jets containing CO2. The Journal of Chemical Physics, 62(2), 341–349.