A time resolved laser study of hydrocarbon chemistry in H-2-CH4 surface wave plasmas

Citation
J. Ropcke et al., A time resolved laser study of hydrocarbon chemistry in H-2-CH4 surface wave plasmas, J PHYS D, 34(15), 2001, pp. 2336-2345
Citations number
58
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science
Journal title
JOURNAL OF PHYSICS D-APPLIED PHYSICS
ISSN journal
00223727 → ACNP
Volume
34
Issue
15
Year of publication
2001
Pages
2336 - 2345
Database
ISI
SICI code
0022-3727(20010807)34:15<2336:ATRLSO>2.0.ZU;2-6
Abstract
Time resolved tunable infrared diode laser absorption spectroscopy has been used to detect the methyl radical and four related stable molecules, CH4, C2H2, C2H4 and C2H6, in H-2 surface wave plasmas (f = 2.45 GHz, power densi ty approximate to 10-50 W cm(-3)) containing 10% methane under static condi tions at different pressures (p = 0.1-4 Torr). For the first time, the time dependence of the conversion of methane to the methyl radical and three st able C-2 hydrocarbons was studied in a fixed discharge volume nearly up to a stationary state. The degree of dissociation of the methane precursor was found to increase by up to 96% in the stationary state, and the methyl rad ical concentration was measured to be in the range of 10(12)-10(13) molecul es cm(-3). The concentrations of both C2H2 and C2H4 produced in the plasma showed a maximum at a distinct time before decreasing. In contrast, the C2H 6 concentration was observed to increase with time to a nearly constant val ue between 6 X 10(12) and 2 X 10(14) molecules cm(-3) varying with pressure . Based on time resolved concentrations, conversion rates to the measured C-2 hydrocarbons (R-C(C2Hy) = 10(11)-10(13) molecules J(-1)) could be estimate d in dependence on pressure in a surface wave discharge. The influence of d iffusion on the spatial distribution of the hydrocarbon concentration in th e discharge tube was considered. A qualitative model has been developed in order to describe the chemical processes and to identify the main plasma ch emical reaction paths.