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

Abstract

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.