1. A fair way to compare shock strength for this purpose is to scale the kinetic energy per molecule (relative to the shock front) according to the ionization potential. Thus, a Mach 10 shock wave in air (I = 9.25 eV for NO; molecular wt = 29) is comparable to a Mach 12 shock wave in argon (I = 15.7 eV; molecular wt = 40).