Two N₂⁺(B² _u⁺) populations with different Boltzmann distribution of the rotational levels found in different types of N₂/Ar discharges—improved estimation of the neutral gas temperature

Abstract

We investigated the rotational excitation of the nitrogen molecule ion in a pulsed magnetron sputter discharge (Mg target, pressure 0.1–2.0 Pa) and a 150 Pa dc glow discharge in dependence on various process parameters. For this purpose we used optical emission spectroscopy of the 0–0 band of the first negative system of the (FNS0–0) and calculated the rotational temperature by fitting the spectra. Often, the best fit could be achieved assuming two populations of the molecules having two different rotational temperatures. These temperatures and their contributions to the spectrum of the FNS0–0 show a significant dependence on the process parameters. The lower temperature is in the range of 370–800 K and is believed to be equal to the translational temperature of the neutral gas. The higher temperature is in the order of 1500–3000 K and its origin is most probably the excitation of the state by heavy particle impact connected with rotational excitation.

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

“…This indicates that there is a significant production of electrons during the recombination phase. One hypothesis is that electrons are created by Penning and associative ionization reactions [40,41,44], see table 2. These ionization processes should take place on a time scale in the order of 100 ns.…”

Spatial distribution of the neutral gas temperature in rf and dc magnetron sputter discharges determined by fitting rotational spectra of the N2+ using a two-temperature fit

“…Then the spectra were fitted using two methods introduced in Ref. [30]. Firstly, a single Boltzmann distribution of the rotational levels was assumed.…”

“…Before a short summary of the two fitting methods the main excitation channels of the N 2 + (B) state in low pressure plasmas should be mentioned (see also Ref. [30] and references given therein). It can be populated by electron impact from the ground state of the neutral N 2 molecule N 2 (X) [35,36] via…”

“…In Ref. [30] the error for the results of the two-temperature fit was estimated. It is V20 K for T rot,1 for all spectra, and V200 K for T rot,2 if the contribution of bhotQ molecules to the spectrum is N15%.…”

“…In Ref. [30] it was shown that for the 0-0 band of the first negative system (FNS0-0) of the N 2 + at least two excitation channels have to be considered in order to obtain a reliable measure for the gas temperature. One excitation channel results in a rotational level distribution according to the neutral gas temperature.…”