Experimental comparison of rotational and gas kinetic temperatures in and He- discharges

Abstract

We report an experimental comparison of the rotational temperature and the gas kinetic temperature of and in a positive column discharge. The discharge is operated in an oven. The oven temperature, determined with a thermocouple, provides a lower bound for the gas kinetic temperature. An upper bound on the temperature is obtained by adding to the oven temperature a calculated increase in the gas temperature due to the discharge. The contribution of the discharge to the gas temperature is calculated under the assumption of complete conversion of input power into gas heating so that the estimate provides an upper bound. The rotational temperature of is determined directly with a Boltzmann plot of the first negative system. For , the ratio of the first minimum to the secondary maximum for the band profile of the second positive system is used to obtain the rotational temperature. We compare experimental spectra with simulated spectra generated under the assumption that the rotational temperature is equal to the minimum and maximum gas kinetic temperatures. The reliability of the rotational temperature as a gas temperature diagnostic under our experimental conditions is discussed for all bands investigated.

Spectroscopic Studies of Diamond Growth

“…We extended some of our earlier work in such techniques. 4 We discovered that benzene, C 6 H 6 , is present in diamond CVD reactors at far higher concentrations than predicted by models. 5 This discovery is an important step toward a more complete understanding of the carbon balance of diamond CVD reactors.…”

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

“…During the collision of two N 2 molecules one of them looses a vibrational quantum which is gained by the other. Thus, the vibrational level population is far from a Boltzmann distribution whereas the rotational levels tend to equilibrate the gas kinetic temperature very quickly [24]. Even for the high vibrational level N 2 (X, m=18) a rotational temperature of 500 K was found in a 2.3 Torrc300 Pa glow discharge [42].…”

“…Thus, the observed population of the rotational levels is determined by the excitation mechanisms and the rotational level population of the electronic states from which the upper electronic state of the chosen molecule band is populated. For a correct temperature determination all excitation channels have to be considered [23][24][25]. This fact is frequently neglected in the literature, where only direct population by electron impact is considered [26,27] or the rotational level distribution of the excited molecule is simply assumed to be a Boltzmann distribution according to the gas temperature [28,29].…”

Ultraviolet Rayleigh Scatter Imaging for Spatial Temperature Profiles in Atmospheric Microdischarges

“…This work focuses on two techniques to noninvasively measure the rotational and translational temperatures respectively of an atmospheric microdischarge, namely the widely published technique of optical emission spectroscopy of the 2 second positive system [11] [12] and a more novel technique introduced here of imaging the Rayleigh scatter [13] from an ultraviolet pulsed laser.…”

“…Contour fitting is required due to the congestion and complicated nature of the band which results in an unresolved rotational spectrum [12]. The rotational temperatures determined from 2 ( 3 Π → 3 Π ) emission have been generally deemed acceptable representations of the 2 ( 1 Π ) ground state gas temperature [11], but it should be noted these analyses depend strongly on an assumption that the rotational distribution of the 2 ( 3 Π ) state is Boltzmann, and identical to that of the 2 ( 1 Π ) ground state. Further analysis of the various vibrational bands within the 2 ( 3 Π → 3 Π ) spectrum often results in the determination of a vibration temperature associated with the discharge [14], which is also subject to the assumption that the internal energy distribution within the 2 ( 3 Π ) and 2 ( 1 Π ) states are identical.…”