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( 3 P) atom and metastable oxygen O 2 ( a 1 Δ g ) 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( 3 P) atoms and O 2 ( a 1 Δ g ) 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 O 2 molecules to produce O − was compensated by detachment of O − with O( 3 P) and O 2 ( a 1 Δ g ). The rate constants of O − detachment with O( 3 P) atoms ) and singlet O 2 ( a 1 Δ g ) molecules ), were determined in the plasma itself for the first time.