Self-consistent kinetic model of the short-lived afterglow in flowing nitrogen

Abstract

A detailed kinetic model for the flowing nitrogen microwave discharge and post-discharge is developed with the aim of gaining a deeper understanding into the processes responsible for the formation of the short-lived afterglow of nitrogen and for the enhancement of the concentration of N 2 (A 3 + u ) metastable, measured at approximately the same position in Sadeghi et al J. Phys. D: Appl. Phys. 34 1779. The present work shows that the peaks observed in the afterglow, for the density of molecules in radiative N 2 (B 3 g ) and N + 2 (B 2 + u ) and metastable N 2 (A 3 + u ) states, can be explained as a result of a pumping-up phenomenon into the vibrational ladder produced by near-resonant V-V energy-exchange collisions, involving vibrationally excited molecules N 2 (X 1 + g , v) in levels as high as v ∼ 35. The present predictions are shown to be in good agreement with the measured concentrations for N 2 (A 3 + u ) metastables and N( 4 S) atoms, and with the emission intensities of 1 + and 1 − system bands of N 2 .

Relaxation of heavy species and gas temperature in the afterglow of a N2 microwave discharge

“…In the time range between ∼0.8 and 20 ms, these values are more than 100 K smaller than the ones reported in Figure 1. , as discussed in [6]. However, for shorter afterglow times, our predicted values for [N 2 (A)] are underestimated, as in [6].…”

“…The present results have been obtained for the same experimental conditions considered in [3,6] corresponding to an afterglow of a flowing microwave discharge with a frequency of 433 MHz produced in a 3.8 cm diameter Pyrex tube at a pressure of 440 Pa. As in [6] we have used in our calculations a value of 3 Â 10 10 cm À3 for the electron density in the discharge and beginning of the afterglow, corresponding to the one experimentally found in [3]. This value is slightly larger than the critical value for the electron density 1.17 Â 10 10 cm À3 , obtained from the…”

“…Other modelling works developed previously with the aim to study the nitrogen afterglow [4][5][6] often consider the gas temperature as an input parameter, either by considering different values for the discharge and postdischarge [4,5] or using experimental results [6]. It is worth noting that the kinetic model presented in [6] considers the same experimental conditions [3] we are adopting in this work.…”

“…It is worth noting that the kinetic model presented in [6] considers the same experimental conditions [3] we are adopting in this work. While the modelling results reported in [6] were principally focused on a very detailed description of the time-dependent kinetics of heavy species, such as N( 4 S), N 2 (A 3 P u + ), N 2 (B 3 ∏ g ) and N 2 (a 0 1 P u ), the main purpose of the present work is the theoretical study of the temporal variation of the gas temperature and its influence on the overall kinetics. To our knowledge, such a theoretical analysis on the afterglow has not been carried out before.…”

“…To shorten this paper to an appropriate length, the reader should refer to references [4][5][6][7]9,11] for more details on collisional data, modelling aspects concerning the electron Boltzmann equation, microwave discharge and post-discharge conditions, to references [1,2,10,11] for additional information on gas heating mechanisms, gas thermal balance equation and energy data, as well as to [1,[13][14][15] for the values of the molar heat capacity and thermal conductivity under non-equilibrium conditions.…”