The kinetics of the reaction of OH With COS

Abstract

The laser/flash‐photolysis laser‐induced fluorescence technique was employed to study the reaction of OH with carbonyl sulfide (COS) in various buffer gases (He, N2, and SF6). In order to determine the relevance of this reaction to tropospheric chemistry the influence of O2 on the rate constant was investigated. To avoid secondary reactions, especially the photolysis of COS, different photolytic OH precursors (H2O2, HNO3, and HONO) with different photolysis light sources (Xe flash lamp, ArF laser, fourth‐harmonic Nd: YAG laser, XeF laser, and third‐harmonic Nd: YAG laser) were used. The rate constant (1.92±0.25)×10−15 cm3 s−1 for the reaction of OH with COS at room temperature was found (after correcting for H2S impurity) to be independent of the pressure and the buffer gas. Addition of O2 was found to have no influence on the measured rate constant. Certain experiments were carried out at 298 K and 245 K to ascertain the mechanism for this reaction. Our results suggest that the degradation pathway involving homogeneous gas phase reaction of COS with OH is of minor importance in the troposphere.