A pulsed laser photolysis-pulsed laser induced fluorescence technique has been employed to study the reaction of OH with CS2 in the presence of He, N2, air, and O2 buffer gases and over the temperature range 250-350 K. In the absence of O2, evidence for rapid, reversible formation of a CS2OH adduct is observed. Analysis of observed OH temporal profiles gives the forward and reverse rates of adduct formation and hence the equilibrium constant. A heat of reaction of -9.9 ± 1.2 kcal mol-1 is obtained from the temperature dependence of the equilibrium constant. The temperature dependence of the bimolecular rate coefficient for the forward addition reaction in 680 Torr of N2 + O2 is well-represented by the Arrhenius expression 6.9 × 10-14 exp(1150/T) cm3 molecule-1 s-1. A rapid reaction of OH with CS2 is observed in the presence of O2, confirming the observations reported in previous competitive rate studies. The observed bimolecular rate constant (kobsd) for the OH + CS2 reaction at 295 K in 700 Torr of air is found to be (1.5 ± 0.1) × 10-12 cm3 molecule-1 s-1; kobsd increases dramatically with decreasing temperature. All experimental observations are consistent with a simple three-step reaction mechanism: adduct formation followed by adduct decomposition in competition with an adduct + O2 reaction. Analysis of our data using a steady-state approximation based on the above three-step mechanism leads to a rate coefficient of (2.9 ± 1.1) × 10-14 cm3 molecule-1 s-1 for the adduct + O2 reaction.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry