Dissociation mechanisms in nitrogen discharges

This work presents a theoretical and experimental investigation of the dissociation rate and N(4S) atom concentrations in a nitrogen DC discharge operating at gas pressures p=0.5–4 Torr and discharge currents I=10–80 mA. By comparing the measured and calculated atomic densities, the various mechanisms for production of N(4S) atoms are discussed and weighted. It is shown that electron impact dissociation controls nitrogen dissociation only at the lower pressures considered in this study. For p≳1 Torr, dissociation proceeds essentially via reactions involving the long-lived metastable heavy-particles N2(X 1Σg+,v) and N2(A 3Σu+), such as 2N2(X,10<v<25)→N2(X)+2N and N2(X,14⩽v′⩽19)+N2(A)→N2(X)+2N. For a gas temperature of 500 K, the rate coefficients for these two reactions are estimated to be of the order of 10−15 and 10−12 cm3/s, respectively.