On the hydrocarbon chemistry in a H-2 surface wave discharge containing methane

Tunable infrared diode laser absorption spectroscopy has been used to detec t the methyl radical and four stable molecules, CH4, C2H2, C2H3 and C2H6, i n a H-2 surface wave discharge (f = 2.45 GHz and power density approximate to 10-50 W cm(-3)) containing up to 10% methane under different flows (Phi = 22-385 seem) and pressures (p = 0.1-4 Torr). The degree of dissociation o f the methane precursor varied between 20% and 85% and the methyl radical c oncentration was found to be in the range of 10(12) molecules cm(-3). The m ethyl radical concentration and the concentrations of the stable cm C-2 hyd rocarbons C2H2, C2H4, C2H6, produced in the plasma, increased with an incre asing amount of added CH4 as well as with increasing pressure. For the firs t time, fragmentation rates of methane (R-F(CH4) = 1 x 10(15-)2.5 x 10(16) molecules J(-1)) and conversion rates to the measured C-2 hydrocarbons (R-C (C2Hy): 5 x 10(13)-3 x 10(15) molecules J(-1)) could be estimated with depe ndence on the flow and pressure in a surface wave discharge. The influence of diffusion and convection on the spatial distribution of the hydrocarbon concentration in the discharge tube was considered by a simple model.