Aachen PK 2003 – scientific programme
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P: Plasmaphysik
P 4: Poster I
P 4.35: Poster
Monday, March 17, 2003, 17:45–19:15, Foyer
New Determination of the Line Strength of the Methyl Radical using a Pulsed Discharge — •G.D. Stancu1, P.B. Davies2, and J. Röpcke1 — 1Institute for Low-Temperature Plasma Physics,17489 Greifswald,Germany — 2Department of Chemistry,University of Cambridge,Cambridge,CB21EW,U.K.
The study of the behaviour of free radicals together with their associated stable products provides an effective approach for understanding chemical phenomena in molecular plasmas. Radicals containing carbon, in particular the methyl radical (CH3), are of special interest for fundamental studies and for applications in plasma technology. The accuracy of calculated methyl concentrations (and hence the validity of plasma chemical modelling based on methyl radical reactions) is directly related to the precision of methyl line parameters. In spite of the importance of the line strength it has only been measured for one line of methyl in the infrared and with an uncertainty of 30 % [1].
This contribution will describe spectroscopic studies of pulsed H2-Ar microwave plasmas (f=2.45 GHz) containing C2H2 or CH4. By combining a planar microwave reactor with an optical multi pass cell the detection sensitivity for transient plasma species by infrared tunable diode laser absorption spectroscopy (TDLAS) has been considerably improved over earlier measurements. Based on time resolved TDLAS measurements the concentration and lifetime of CH3 has been measured directly leading to accurately determined line strengths of several absorption lines of CH3 around 16 µm.
[1] Wormhoudt J et al. 1989 Chem. Phys. Lett. 156, 47.