CH3CH2SCH3+OH radicals: Temperature-dependent rate coefficient and product identification under atmospheric pressure of air

Abstract

Relative rate coefficients have been determined for the gas-phase reaction of hydroxyl (OH) radicals with ethyl methyl sulfide (EMS) using isobutene as a reference compound. The experiments were performed in a 1080 L quartz glass photoreactor in the temperature range of 286-313 K at a total pressure of 760W10 Torr synthetic air using in situ FTIR absorption spectroscopy to monitor the concentration-time behaviors of reactants and products. OH radicals were produced by the 254nm photolysis of hydrogen peroxide (H2O 2). The kinetic data obtained were used to derive the following Arrhenius expression valid in the temperature range of 286-313 K (in units of cm3 molecule-1 s-1): k = (3.0±0:6) × 10-15 exp [(2457 ± 65)/=T]The rate coefficient displays a negative temperature dependence and low pre-exponential factor which supports the existence of an addition mechanism for the reaction involving reversible OH-adduct formation. The results are compared with previous data of other sulfides from the literature and are rationalized in terms of structure-reactivity relationships. Additionally, product identification of the title reaction was performed for the first time by the FTIR technique under atmospheric conditions. Sulfur dioxide, formaldehyde, and formic acid were observed as degradation products in agreement with the two possible reaction channels (addition/abstraction). Copyright © 2010 John Wiley and Sons, Ltd.