Tunable Diode Laser Diagnostic Studies of H2-Ar-O2 Microwave Plasmas Containing Methane or Methanol

Tunable infrared diode laser absorption spectroscopy has been used to detect the methyl radical and ten stable molecules in H₂-Ar-O₂ microwave plasmas containing up to 7.2% of methane or methanol, under both flowing and static conditions. The degree of dissociation of the hydrocarbons varied between 30 and 90% and the methyl radical concentration was found to be in the range 10 ¹⁰ –10 ¹² molecules cm ^–3 . The methyl radical concentration and the concentrations of the stable C-2 hydrocarbons C ₂ H ₂ , C ₂ H ₄ , and C ₂ H ₆ , produced in the plasma decayed exponentially when increasing amounts of O ₂ were added at fixed methane or methanol partial pressures. In addition to detecting the hydrocarbon species, the major products CO, CO ₂ , and H ₂ O were also monitored. For the first time, formaldehyde, formic acid, and methane were detected in methanol microwave plasmas, formaldehyde was detected in methane microwave plasmas. Chemical modeling with 57 reactions was used to successfully predict the concentrations in methane plasmas in the absence of oxygen and the trends for the major chemical product species as oxygen was added.     

Density Distribution of Plasma Species in a Hollow Cathode Arc Discharge for Coating Application

The plasma of a hollow cathode arc discharge (argon/titanium) was studied by emission spectro-scopy and probe measurements. The behavior of the relative particle concentrations of the different heavy plasma components as well as the concentration and temperature of the electrons was determined as function of the vertical distance from the anode crucible. Abel-inverted radial distributions of the relative level populations for TiI (neutral titanium), TiII (singly ionized titanium), Ar I and ArII are presented. Further measurements characterize the influence of the discharge current on the relative level population.