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

A spatially averaged (well mixed) reactor model was used to simulate a powe r-modulated (pulsed) high density oxygen discharge. Chemistry involving the high energy oxygen metastable molecules O-2(M)(A (3)Sigma(u)(+)+C (3)Delta (u)+c (1)Sigma(u)(-)) was included in the simulation. This chemistry was ne cessary to capture the experimentally observed increase in the O- negative ion density in the afterglow of the pulsed discharge. As the electron tempe rature drops in the afterglow, the rate coefficient of electron attachment with O-2(M) increases several fold. The wall recombination probability of o xygen atoms affected the O- density drastically. For the conditions studied , the maximum O- density in the afterglow increased with pressure, decrease d with power, and showed a maximum with pulse period. The time in the after glow at which the peak O- density occurred decreased with pressure and powe r, and was independent of the pulse period. Knowing the temporal evolution of O- in the afterglow may be important for applications requiring extracti on of negative ions out of the discharge. (C) 2000 American Institute of Ph ysics. [S0021-8979(00)07512-5].