Theoretical study of the role of ultraviolet radiation of the non-equilibrium plasma in the dynamics of the microwave discharge in molecular nitrogen

Abstract

A self-consistent plasmachemical model describing the dynamics of the non-equilibrium microwave discharge in molecular nitrogen with consideration for kinetic, photochemical and electrodynamic phenomena is proposed. The photochemical block of the model accounts for the processes of photoexcitation and photoionization of nitrogen molecules in the ground and excited electronic states. Radiative emittance of the discharge plasma is conditioned by the processes of photorecombination of electrons and positive ions as well as by the processes of spontaneous radiation of electronically excited molecules. Solution of radiation transfer equations and calculation of photochemical constants were made with allowance for the vibrational-rotational structure of the corresponding radiative transitions. The calculations performed have shown that the velocities of the ionization front propagation in the microwave discharge that were observed experimentally may be explained without invoking considerations concerning the existence of easily ionizable admixtures in nitrogen. The phenomenon of electron generation in the photohalo region of the discharge is mainly conditioned by the processes of stepwise photoionization of nitrogen molecules. The mechanisms leading to the development of kinetic instabilities in the discharge region are analysed, and a satisfactory agreement between calculation and experimental results is noted.

Formation of vibrational distribution function of electronically-excited N2(A , v) molecules in nitrogen discharge plasma

“…For example, about 2 eV must go to a gas heating in the quenching process of N2(a 1 Пg) state with the excitation energy of 8.6 eV. This assumption [3] is inconsistent with the experimental results [14][15][16], where the authors showed that the energy transfer between electronically excited N2 molecules occur with minimal energy release converted to the translational degrees of freedom of reaction products. Therefore the problem of fast gas heating in nitrogen discharge plasma still remains open.…”

“…lectronically excited N2(A 3 Σ u + ,v) molecules play an important role in gas discharge kinetics in nitrogen and nitrogen-oxygen mixtures [1][2][3][4][5][6][7][8]. In mixtures with a small fraction of oxygen a considerable part of the discharge energy, spent on excitation of electronic degrees of freedom, accumulates in N2(A 3 Σ u + ) state.…”

“…The population of N2(A 3 Σ u + , v) state in nitrogen discharge plasma occurs mainly due to the radiativecollisional quenching of N2(В 3 Пg), N2(B' 3 Σ u − ), N2(W 3 ∆u) molecules [1][2][3][4]. Quenching of N2(В 3 Пg,v) by nitrogen molecules N2(Х 1 Σ g + ) has been investigated in [10][11][12].…”

“…The obtained rate constants of quenching of N2(A 3 Σ u + ,v = 0÷7) levels were widely used in all main kinetic models of nitrogen discharge plasma [1][2][3][4][5][6]8] and others.…”

“…This phenomena has been fixed in experiments [18][19][20] but had no theoretical validation yet [21]. In [3] the processes of gas heating, associated with quenching of the electronically excited nitrogen molecules, were investigated. It was assumed there, that at deactivation of N2 electronic states with excitation energy εex higher than 6.6 eV (the excitation energy of the N2(A 3 Σ u + ,v=3,4) state), the total energy release ε = εex -6.6 eV is spent on the gas heating.…”