Emission spectrometry of NO or activated nitrogen species in non-thermal plasma

Abstract

Emission spectrometry in the atmospheric pressure discharge was carried out to understand reaction mechanisms of active species, as the discharge plasma processing is significantly influenced by the gas components. The N/sub 2/ second positive band (SPB), the N/sub 2/ first negative band (FNB) and the NO-/spl gamma/ band were investigated using a digital controlled spectrometer and an ICCD camera. When dielectric pellets were placed between a needle-plate type electrode, these emissions decreased along with the electrode axis. In the positive streamer discharges of needle-plate electrodes, high-energy electrons were mainly produced around the tip of the needle electrode leading to the N/sub 2/ first negative band. When the discharge energy exceeded a certain value, the intensity of the N/sub 2/ first negative band increased, compared to other bands. This is due to the presence of high-energy electrons below the needle electrode and on the dielectric plate. The emission spectrum observation with time resolution allowed us to conclude that the N/sub 2/ second positive band emission and that of N/sub 2/ first negative band emission were extinguished within 200 ns, while that of NO-/spl gamma/ band continued for more than 3 /spl mu/s. This could be due to a difference in the mechanisms of light emission. N/sub 2/ second positive band and N/sub 2/ first negative band were excited by electron collisions, while NO-/spl gamma/ band was energized by collisions of N/sub 2/(A)-state molecules. Distribution of NO molecules in the corona discharge or the barrier discharge was obtained from a decay constant of NO-/spl gamma/ band emission. NO could be decomposed by a reducing reaction at the tip of the needle in the corona discharge. On the contrary, NO could be decomposed by a reducing reaction around the plate electrode in the barrier discharge.