Effect of metastable oxygen molecules in high density power-modulated oxygen discharges

Abstract

A spatially averaged (well mixed) reactor model was used to simulate a power-modulated (pulsed) high density oxygen discharge. Chemistry involving the high energy oxygen metastable molecules OM2 (A 3Σ+u + C 3Δu + c 1Σ-u) was included in the simulation. This chemistry was necessary to capture the experimentally observed increase in the O- negative ion density in the afterglow of the pulsed discharge. As the electron temperature drops in the afterglow, the rate coefficient of electron attachment with OM2 increases several fold. The wall recombination probability of oxygen atoms affected the O- density drastically. For the conditions studied, the maximum O- density in the afterglow increased with pressure, decreased with power, and showed a maximum with pulse period. The time in the afterglow at which the peak O- density occurred decreased with pressure and power, and was independent of the pulse period. Knowing the temporal evolution of O- in the afterglow may be important for applications requiring extraction of negative ions out of the discharge. © 2000 American Institute of Physics.