Gas molecule dissociation effect on rf discharge burning in low pressure ammonia

This Letter outlines the experimental study of molecule dissociation effect on rf capacitive discharge burning. We show that for each ammonia pressure value there exists some threshold rf voltage value below which the dissociation degree does not exceed 3%, but at higher rf voltage it grows to 30%. Increasing NH₃ dissociation degree accelerates the discharge current growth against rf voltage. The rf discharge remains in a weak-current α-mode at low as well as at high dissociation degree because all ammonia dissociation products possess ionization potentials exceeding that for NH₃.