Oxygen atom actinometry reinvestigated: Comparison with absolute measurements by resonance absorption at 130 nm

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Abstract
Resonance absorption at 130 nm was used to measure absolute oxygen atom concentrations in O2-containing distributed electron cyclotron resonance plasmas. The dissociation fraction [O]/[O2] in pure O2 plasmas (1–6 mTorr) was in the range 0.01–0.06, but was significantly increased by the addition of SF6, N2 or Kr. At 2 mTorr total pressure a maximum [O]/[O2] of 0.3 was observed for 10% SF6 added. The results were compared to those obtained by optical emission actinometry measurements. The quantity I0 (844 nm)/IAr (750 nm) (with 0.1 mTorr Ar added) was poorly correlated with [O] but well correlated with [O2]. This suggests that, for dissociation fractions lower than 0.1, dissociative excitation, O2+e→O*(3p 3P)+O, is the most important mechanism for the production of 844 nm emission.