We use a global (volume averaged) model to study the presence of negative i
ons and metastable species in low-pressure high-density oxygen discharges.
We find the negative oxygen ion O- to be the dominant negative ion in the d
ischarge, the density of the negative ion O-2(-) to be small and the densit
y of the negative ion O-3(-) to be negligible in the pressure range of inte
rest, 1-100 mTorr. Dissociative attachment of the oxygen molecule in the gr
ound-state O-2((3)Sigma (-)(g)) and the metastable oxygen molecule O-2(a(1)
Delta (g)) are the dominating channels for the creation of the negative ox
ygen ion O-. At low pressure (<5 mTorr) recombination involving O- and O+ i
ons is the main loss channel for O- ions. At higher pressure, the detachmen
t on O(P-3) becomes the main loss channel for the O- ion. The creation of O
-2(-) is mainly through dissociative attachment of ozone O-3, Ozone is almo
st entirely created through detachment by the collision of O- with the meta
stable oxygen molecule O-2(a(1)Delta (g)). The creation of O-2(-) is thus g
reatly influenced by this detachment process and neglecting the detachment
has a significant influence on the density of O-2(-) ions. At low pressure
(< 10 mTorr) the O-2(-) ion is mainly lost through recombination while at h
igher pressure the charge transfer to form O-2 is the dominating loss proce
ss.