Dynamics of reactions of O(³P) atoms with CS, CS₂ and OCS

The reactions of CS(X ¹Σ⁺), CS₂(X ¹Σ⁺ _g) and OCS(X ¹Σ⁺) with O(³P) were studied at 298 K by means of a CO laser resonance absorption technique. The CO(ν) population distribution produced from the reaction O(³P) + CS(X ¹Σ⁺) studied in a quartz flash photolysis tube (λ >/ 200 nm) is similar to distributions observed previously for ν > 7. For ν < 7 an energetically colder vibrational population was observed which is attributed to the reaction of O(³P) atoms with undissociated CS₂(X ¹Σ⁺ _g). Subsequent experiments carried out in a Pyrex flash photolysis tube (λ >/ 300 nm) in which the O(³P) + CS₂(X ¹Σ⁺ _g) reaction is the only one which can occur confirmed that the colder population observed is attributable to this process. The branching ratio for the reaction channel O(³P) + CS₂(X ¹Σ⁺ _g) → CO(X ¹Σ⁺) + S₂(³Σ^- _g) has been measured. We find that 1.4 ± 0.2% of the O + CS₂ reaction proceeds through this channel, and that the rate constant for this reaction channel is, k = 3.5 (±0.5) × 10¹⁰ cm³/mole s. Isotope labeled experiments using ¹⁸O atoms show that the O(³P) + OCS(X ¹Σ⁺) reaction takes place by a direct stripping mechanism, wherein CO(ν) is produced exclusively from the parent OCS molecule. The CO(ν) formed in this reaction carries about 9% of the total available energy.