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Negative ion destruction by O(3P) atoms and O2(a 1Δg) molecules in an oxygen plasma

Laser photodetachment was used to investigate the dynamics of negative ion density in the positive column of a pure oxygen dc glow discharge over a range of pressure (0.1–5 Torr) and current density (2–40 mA cm−2). Upon discharge current modulation, the negative ion O− concentration decayed with the characteristic loss times of oxygen O(3P) atom and metastable oxygen O2(a 1Δg) molecule concentrations over a wide range of discharge parameters. To determine the rate constants of negative ion loss by reaction with these species, the dynamics of O(3P) atoms and O2(a 1Δg) molecules was investigated using time-resolved actinometry and IR spectroscopy at 1.27 µm, respectively. At pressures greater than ∼0.5 Torr the attachment–detachment dominated regime of the oxygen discharge was realized and the main negative ion was O−. Under these conditions, electron attachment to O2 molecules to produce O− was compensated by detachment of O− with O(3P) and O2(a 1Δg). The rate constants of O− detachment with O(3P) atoms ) and singlet O2(a 1Δg) molecules ), were determined in the plasma itself for the first time.