Düsseldorf 2007 – scientific programme
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P: Fachverband Plasmaphysik
P 22: Poster
P 22.18: Poster
Thursday, March 22, 2007, 16:30–18:30, Poster A
Investigation of molecular temperature and density trends in methane discharges by means — •Ivonne Möller1, Christiane Rüth1, Anna Serdyuchenko1,2, and Henning Soltwisch1 — 1Institut für Experimentalphysik V, Ruhr-Universität Bochum, 44780 Bochum, Germany — 2present address: University of Nevada, Reno, USA
Absorption spectroscopy using tunable diode lasers is often employed to analyse the chemical composition of reactive plasmas. The interpretation of the measured absorption profiles and the resulting molecular densities are strongly influenced by temperature effects. During the first seconds, in which the plasma is switched on or off, the electron temperature or, more general, the electron distribution function, as well as the translational and the rovibrational temperature of the molecules are not constant.
In this work we investigate the interconnection between theses temperature effects and the measured CH4, C2H2 and C2H6 densities in a pure methane plasma. During the switch-on phase a sudden decrease of the CH4 density has been found, which can be explained by an assumed rise of the translational and rovibrational temperature of about 50 K. During the plasma-off phase the CH4 density can exhibit a two-step increase lasting for up to 40 s. This behaviour cannot be explained so far. A systematic study of the different effects is in progress.