| Abstract
| - OCS formation by the reaction of inorganic polysulfideswith carbon monoxide, which are both abundant in naturalaquatic systems, was studied as a model abiotic routefor OCS formation in the dark. The net OCS accumulationrate was a function of a bimolecular formation reactionand simultaneous OCS hydrolysis kinetics. The reaction ofpolysulfides with CO in the dark was found to be firstorder with respect to CO concentration and first order withrespect to the molar sum of the polysulfide speciesgenerated by the disproportionation of the dissolvedpolysulfide precursors. The pH dependence of the OCSproduction rate was controlled by the pH-dependentdisproportionation of polysulfide precursors. Lowertemperatures, intermediate redox potentials, and moderatelybasic pH conditions increase the steady-state concentrationof OCS. The speciation of polysulfides in aqueoussolutions is still disputed. Some authors claim thathexasulfide is one of the dominant species while othersbelieve that pentasulfide is the largest sulfide species inaqueous systems. Despite the disagreement between differentmodels for speciation of polysulfides, the proposed ratelaw agreed very well with the thermodynamic data basedon four and on five polysulfide species, with only minordifferences in the preexponential kinetic coefficients.
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