Estimates of Shock-Tube Precursor Infrared Excitation

A simple analysis is given for pre-excitation of molecular species in shock-tube flows by precursor infrared radiation. Estimates of rough magnitudes are given under shocked-gas temperature and pressure conditions corresponding to a Mach 5.5 shock propagating into 200 Torr of a 5% test gas, 95% argon mixture. It is found that the effect is slight for species of moderate infrared emission, such as CO, while it may be of some significance for species of high infrared emission, such as CO2.