Interaction of thermal plasma jet with a cold gas was investigated using optical emission spectroscopy. An oxygen-hydrogen thermal plasma jet was generated in the plasma torch with dc electric arc stabilized by water vortex. The plasma jet is characterized by very high temperature and velocity, and low density. An entrainment of ambient air into the jet and mixing of argon injected inside the exit nozzle with the oxygen-hydrogen plasma was studied
by analyzing the distribution of emission of OI, ArI and NI spectral lines within the jet. Emission coefficients obtained with the help of asymmetrical Abel inversion, together with the temperature derived from Hβ and 0II lines, were used to assess the relative mole fractions of atomic oxygen, argon and nitrogen.