Shock-Tube Study of Vibrational Energy Transfers in the CO₂-N₂ and the CO₂-CO Systems

The vibrational relaxation of CO 2 in N 2 and CO has been studied by monitoring the infrared emissions from mode ν 3 of CO 2 and CO behind shock waves in the temperature range of 800-2500 K. The experimental results are explained by the relaxation equation derived in terms of three main energy transfer processes: (1) CO 2 * (ν 3 )+B→Co 2 * (ν 1 , ν 2 )+B, (2) CO 2 * (ν 3 )+B→CO 2 +B * , and (3) CO 2 * (ν 1 , ν 2 )+B→Co 2 +B, where B=N 2 or CO. The rate constant for Process (1) has a temperature dependence in agreement with the theoretical prediction from the short range force theory, though its value is much larger than the theoretical one. The rate for Process (2) in collisions with N 2 shows a negative temperature dependence in a lower temperature region and a positive in a higher region, and a minimum is found in the vicinity of 1300 K. While, the corresponding rate for CO has a weakly positive temperature dependence. These rate constants for Processes (1) and (2) can be connected smoothly to the data of the laser fluorescence measurements in the lower temperature region.