Argon gas was expanded in a supersonic nozzle after being partially ionized by a high-energy electric arc. The frequency of arc voltage oscillation was found to be inversely proportional to the power input to the arc. This was probably due to the motion of the arc with the vortex flow in the arc chamber. When a parallel resonant circuit was inserted in series with the arc, significant oscillation occurred over a range of frequencies from 15 KC to 30 KC. The energy exchanged between the coil and capacitor of the parallel resonant circuit was calculated. Due to the small magnitudes of the oscillation energy and the relatively low frequencies, it was concluded that the magnetic induction of the coils used could not produce any detectable excitation of the gas.