Absorption spectroscopic studies of carbon dioxide conversion in a low pressure glow discharge using tunable infrared diode lasers

The time and spatial dependence of the chemical conversion of CO₂ to CO were studied in a closed glow discharge reactor (p = 50 Pa, I = 2-30 mA) consisting of a small plasma zone and an extended stationary afterglow. Tunable infrared diode laser absorption spectroscopy has been applied to determine the absolute ground state concentrations of CO and CO₂. After a certain discharge time an equilibrium of the concentrations of both species could be observed. The spatial dependence of the equilibrium CO concentration in the afterglow was found to be varying less than 10%. The feed gas was converted to CO more predominantly between 43% and 60% with increasing discharge current, forming so-called quasi-equilibrium states of the stable reaction products. The formation time of the stable gas composition also decreased with the current. For currents higher than 10 mA the conversion rate of CO₂ to CO was estimated to be 1.2×10¹³ molecules J^-1. Based on the experimental results, a plasma chemical modelling has been established.