Collisional quenching of 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.