The structure of shock fronts in various gases

The optical reflectivity of shock fronts in A, N2, O2, CO, CO2, N2O, CH4, Cl2 and HCl have been studied. The thickness of shock fronts in A up to the Mach number M = 1·55 is in agreement with the theory of Gilbarg and Paolucci. The rotational relaxation time is about 5·5 collisions in N2 and equal to or less than that in the other gases. However, for stronger shocks N2 does not appear to reach rotational equilibrium in the shock front and a qualitative theoretical discussion of this phenomenon is presented. In HCl there appears to be over-excitation of rotation in the shock front. There is no vibrational excitation of any of the gases.