Nitrogen vibrational excitation in a N₂/He pulsed planar-ICP RF discharge

Abstract

A pure inductive regime of pulsed RF discharge in N 2 -He mixtures at 0.2 Torr has been investigated by time resolved Langmuir probe and optical emission spectroscopy. A planar coil ICP with a Faraday shield has been used. Mixture compositions of 5-100% N 2 and duty cycles, T ON = 1-15 ms and T OFF = 15 ms, have been explored. The Langmuir probe analysis evidences a Maxwell electron energy distribution in the discharge and post-discharge, characterized by electron density and temperature that depend on both duty cycle and composition. The vibrational excitation of N 2 (C) state is inferred by the N 2 second positive emissions. Its kinetic analysis reveals the formation of a high vibrational excitation of ground state nitrogen. A vibrational temperature higher than 10 000 K can be reached at the end of the 5 ms discharge pulse on the levels v = 0-3 of the X state. Such a high vibrational temperature slows the post-discharge relaxation of the electron temperature.

Characterization of direct current He-N2 mixture plasma using optical emission spectroscopy and mass spectrometry

“…20 The principal species observed were: at 337.13 and 357.69 nm for N 2 (C 3 P u À B 3 P g ) second positive system (SPS); at 391.44 and 427.81 nm for N 2 þ (B 2 R u þ À X 2 R g þ ) first negative system (FNS); at 501.57, 587.56, and 667.82 nm for He. The SPS and FNS were observed by Ambrico et al 21 during pulsed RF discharge in He-N 2 mixtures at 0.2 Torr, which are in good agreement with the experimental results obtained in the present study, although the discharge techniques in both the cases are different. Furthermore, to gain deeper insights on the effect of the intensity variation of species as a function of the He percentage, we analyzed the evolution of each component as a function of He percentage, normalizing their intensities (I x / P I x ).…”

“…21,23,34,35 Therefore, considering the experimental conditions adopted in the present study, the important processes of inelastic electron-atom, electron-molecule, and subsequent emission transitions from excited states are…”

Time-resolved optical emission spectroscopy of nanosecond pulsed discharges in atmospheric-pressure N2 and N2/H2O mixtures

“…A typical value of the electron temperature in a thermal atmospheric pressure plasma with a high electron density is 15000 K [33]. Due to reactions of electrons with vibrationally excited N 2 in the afterglow the electron temperature follows normally the vibrational temperature rather than dropping immediately to the gas temperature [34][35][36]. Therefore an electron temperature of 10000 K is assumed in the spark and recombination phase and since T e > T g , 2500 K is taken as a lower estimate of T e .…”

Formation and Excitation of CN Molecules in He–CO–N2–O2 Discharge Plasmas

“…The relation between the N 2 vibrational temperatures in the ground and excited states has been investigated and discussed by many authors, see e.g. [57][58][59][60][61][62][63][64]. These temperatures may differ significantly and their relation is rather complicated when there are more excitation channels, including the process: N 2 ðAÞ þ N 2 ðAÞ !…”

“…in [61,63,64] that in the pure nitrogen discharges (with CO admixture in afterglow) the last process plays the most important role in N 2 (C) excitation and its neglect lead to significant errors. However, it plays negligible role under conditions considered here, i.e.…”