Optical emission spectroscopy is used to characterize the production of active species as a function of hydrogen concentration in the mixture under different operating conditions. A major concern is to enhance the concentration of the active species by hydrogen addition that carry several electron volts energy above their ground states, and thus affect the surface chemistry. The emission intensity of the selected optical transitions of molecular and atomic species is measured to determine the functional dependence of their radiative states. The relative ground state molecular ion density [N2 +]is measured from the emission intensity of the first negative band head (λ = 391.4 nm, 0–0) by considering the fact that in low temperature plasma, ion with single charge is produced by the electron impact, and the ion density is proportional to the electron density. It is found that the concentration of the active species may be enhanced significantly by selecting an appropriate gas composition and operating parameters. The SS-304 samples are nitrided under the optimum conditions for 4, 8, 12 and 16 hours and hardness values are found to increase five times for 16 hours treatment time. The optimized discharge conditions are found favorable for plasma ion nitriding.