Collisional quenching of $\boldsymbol{{{{\rm N}}_{2}}({{{\rm A}}^{3}}\Sigma _{u}^{+})}$ by three xylene isomers and prevention of discharge current induced by film deposited on cathode by decomposion of xylene

Abstract

Determination of the effective lifetime of in N2 with an admixture of a small amount of xylene (dimethylbenzene C6H4(CH3)2) was carried out by waveform analysis of the transient current after turning off the UV light in a Townsend discharge. Xylene has three isomers (o-, m- and p-), and the collisional quenching rate coefficients of by these isomers were determined together with the diffusion coefficients of and the reflection coefficients of on an electrode surface. We found that the obtained collisional quenching rate coefficients of by o-, m- and p-xylene are considerably different as (2.3 ± 0.3) × 10−10, (4.4 ± 0.6) × 10−10 and (6.5 ± 0.9) × 10−10 cm3 s−1, respectively. During repeated measurements, we observed variations of the ionization process in the admixtures, which appeared as distorted transient current waveforms with fluctuation, making it impossible to continue the experiment to determine the three coefficients. The results suggest that the electron emission from the surface of the cathode is prevented by a deposited substance covering the cathode. This substance on the surface was identified as CHn (n = 1, 2, 3), which split from the benzene ring of the xylene molecules.

Experimental derivation of Arrhenius equations for collisional quenching rate coefficients of Ar(3P2) by Ar(1S0) and H2O

“…Here, γ m is the secondary ionization coefficient for the metastables at the cathode, the so-called γ m -action [9][10][11][12], and p k (t) is a function of time, with the incident flux to the cathode of the diffusing metastable molecules produced by an electron leaving the cathode at t = 0.…”

“…Figure 2 shows the experimental apparatus used in the study, which has been described in detail elsewhere [9][10][11][12]. A pair of gold-plated plane parallel electrodes with an effective diameter of 8.0 cm were mounted in the central part of a chamber.…”

“…In this paper, we present experimentally obtained values of the collisional quenching rate coefficients of the metastable excited atom Ar( 3 P 2 ) by Ar( 1 S 0 ) and H 2 O following our previous investigation on N 2 A 3 Σ + u [9,10,11] and Ne( 3 P 2 ) [12] in the Townsend discharge (TD). These were determined by a nonspectroscopic method based on waveform analysis, for which the original theory was established by Molnar [13,14] and improved by us [9].…”