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.