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.

Measurements have been made in a shock tube of the hot-flow duration, the structure of the contact front, and the nature of the mixing zone. The flow duration was obtained by spectroscopically detecting the first arrival of the driver gas, and is observed to become vanishingly small with decreasing initial driven gas pressure. These data and the data of Roshko and Duff are compared with predictions of Roshko's (laminar) theory and the numerical example of Anderson's (turbulent) theory. Agreement with the one point of Anderson's prediction is surprisingly good, while the agreement with Roshko's theory ranges from excellent to unsatisfactory. Approximations in Roshko's treatment which contribute to the lack of correlation with the data obtained in the smaller diameter shock tubes of Duff and the present work are emphasized and a formulation of the flow model is developed which better predicts the actual shock-tube flow durations.

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