(19,22) In particular, the kinetics of the reaction of For that reason, a great number of different experimental instruments and techniques have been used to take into account all possible reaction pathways in the atmosphere, and our study will follow that example.ĭetailed studies on the kinetics of the gas-phase oxidation of sulfur compounds, both organic and inorganic, can be found in many previous publications that are summarized in two important review papers. This indicates that the mechanism of DMS oxidation is very complex and not completely understood and that the branching ratios are strongly dependent upon environmental conditions and presence of clouds. Moreover, Mardyukov and Schreiner (19) studied five different DMS oxidation mechanisms and compared them with nine different field measurements, concluding that no single mechanism reproduced the observations and predictions. NO 3 mechanisms of oxidation of DMS do not fully account for diurnal decay rates typically observed in the MBL.(15−17) A relatively recent review and critical assessment of 20 different models and their uncertainties by Faloona (18) concluded that the standard (10−14) The identity and yields of the final products depend on the oxidation steps of several intermediates for which a multitude of different possible reaction pathways may exist, whose importance can vary with the prevailing atmospheric conditions.
OH radicals leads to the formation of a variety of sulfur-containing end products, with the most important being DMSO, sulfur dioxide (SO 2), MSA, sulfuric acid (H 2SO 4), and dimethylsulfone (DMSO 2).From the interplay of thermochemical and kinetic arguments, it was possible to demonstrate that the preferred product of the reaction of dimethyl sulfide with two hydroxyl radicals is actually dimethyl sulfoxide. According to our best results, the initial methyl thiomethyl radical was obtained at −25.2 kcal/mol (experimentally −22.4 kcal/mol), and four important paths were identified on the potential energy surface. The rate coefficient for abstraction affords a 4.72 × 10 –12 cm 3 molecule –1 s –1 value, very close to the most recent experimental one (4.13 × 10 –12 cm 3 molecule –1 s –1). Additionally, important rate coefficients were computed using canonical and variational transition state theory. In this work, we performed a computational study using quantum-chemical methods, of the mechanism of H-abstraction from dimethyl sulfide under normal atmospheric conditions and in reaction chambers at different O 2 partial pressure, including complete absence of oxygen.
Although the reaction of intermediate species with additional hydroxyl radicals has been considered as part of the global mechanism of oxidation, little if any attention has been dedicated to the possibility of reactions of the initial radicals with a second
Most frequently, theoretical studies of the addition and H-elimination reactions of dimethyl sulfide with hydroxyl radicals are studied considering the presence of oxygen that further reacts with the radicals formed in the initial steps. Elucidation of the oxidation mechanism of naturally emitted reduced sulfur compounds, especially dimethyl sulfide, plays a central role in understanding background acid precipitation in the natural environment.