Mechanism of N$_{2}$ Dissociation and Kinetics of N($^{4}$S) Atoms in Pure Nitrogen Plasma*

This work deals with kinetics of the ground state nitrogen atoms N($^{4}$S) and N$_{2}$ dissociation mechanism in pure N$_{2}$ plasma. The experiment was carried out in positive column of DC glow discharge for p$=$5-50Torr, J$=$20-100mA. N($^{4}$S) balance was considered for spatially uniform conditions controlled by only two terms: source (characterized by effective production rate k$_{eff}$ ) and loss (characterized by effective loss time $\tau_{loss} )$. Analysis of k$_{eff}$ and $\tau_{loss} $ gains considerably better understanding of N$_{2}$ dissociation. N/N$_{2}$ dissociation rate as function of discharge parameters was obtained using two independent optical methods: actinometry on Ar atoms and N$_{2}$2$+$ band emission decay at discharge modulation. With N/N$_{2}$ radial profiles N atom surface loss probability $\gamma_{N}$ and then $\tau_{loss} $were estimated. $\gamma_{N}$ revealed to be dependent on N($^{4}$S) concentration and thereby discharge conditions through the sorption balance of physisorbed N atoms. Phenomenological model taking into account basic surface processes provides $\gamma_{N}$ data in good agreement with experiment. Finally, k$_{eff}$ was obtained as function of E/N and it was shown that even EEDF calculated with accounting for N$_{2}$ vibrational excitation is unable to provide observed values of k$_{eff}$. Reasons of that fact are discussed in detail.