Formation of CN in N2 + He discharges in graphite hollow cathodes

Abstract

Carbonaceous vapour created by nitrogen and helium discharges in graphite hollow cathodes has been investigated to identify the mechanisms for CN formation. The characteristics of hollow cathode discharge have been exploited to provide the two-energy-regime electrons that initiate a complex process for the production of ions and metastable atoms and molecules of He and N2. These introduce the sputtered carbon species Cx (x ≥ 1) from the graphite cathode. Dominant among the Cx species are C1 and C2 that are excited and participate in inter- and intra-species collisions. CN, therefore, is the direct by-product of reactions between sputtered C and N2. From the optical emission spectra the level densities of nitrogen and helium were recorded during the cycling of discharge current idis of the graphite hollow cathode. The emission spectra are dominated by strong emission bands of CN (violet system Δν = −1, 0, +1) and N2 (2nd positive system), along with the atomic lines of He and C. We have identified and suggested a mechanism for the formation of CN in nitrogen plasmas in graphite hollow cathodes.