Shock-Tube Study of Vibrational Relaxation in Carbon Monoxide for the Fundamental and First Overtone

Abstract

The rate of vibrational excitation in rapidly heated CO has been determined for the temperature range 1100°—2500°K by observation of infrared emission behind incident shocks. Great care was taken to eliminate impurity effects. The data agree to within 15% with those of Matthews. Separate observations of fundamental and overtone emission demonstrated that excitation occurs in a stepwise fashion. Collisional population of the v=2 level by successive single quantum transition is at least ten times faster than the direct 0→2 excitation process. Vibrational relaxation times of CO were determined for the pure gas and for the mixtures; 5% CO—95% Ar, 5% CO—95% N₂, and 99% CO—1% H₂. At 2000°K, τ(CO–CO) = 60 μsec, τ(CO–Ar) = 350 μsec, τ(CO–N₂) = 640 μsec, τ(CO–H₂) = 0.7 μsec, all for one atmosphere total pressure with the CO infinitely dilute in the second‐named gas. The differences found between CO–CO collisions and CO–N₂ collisions with respect to vibrational excitation are not explained by current theories.