Formation pathways of DMSO from DMS‐OH in the presence of O₂ and NO_x: A theoretical study

Abstract

The relative importance of the reaction pathways and thus the product yields in the dimethyl sulfide (DMS) degradation scheme initiated by the hydroxyl (OH) radical has been said to be influenced by the content of nitrogen oxides (NO(x)) in chamber experiments. In this study, ab initio and density functional electronic structure calculations of all the possible reaction pathways corresponding to the reaction process initiated by DMS-OH + oxygen (O(2)), leading to the formation of the dimethyl sulfoxide (DMSO) product in the presence of NO(x) (NO and NO(2)), are carried out for the first time. The results for the different pathways are compared with the objective of inferring their kinetic relevance in the laboratory experiments that measure DMSO formation yields. Our theoretical results clearly show the existence of NO(x)-dependent pathways leading to the formation of DMSO in addition to O(2)-dependent channels. So then, NO(x)-containing conditions would have to modify the relative importance of the addition channel in the DMS oxidation process.

Variational transition‐state theory study of the rate constant of the DMS·OH scavenging reaction by O2

“…37,39 In those studies, the stationary points found were characterized at both the MPW1K/6-311G(d,p) and the MPW1K/MG3S levels of calculation. Those stationary points were connected by means of the corresponding MEPs calculated with the smaller basis set.…”

“…According to the conclusions obtained in a previous work 32 and maintaining the methodology used in our recent electronic structure studies, [37][38][39] the MPW1K/MG3S level of calculation has been chosen for the description of the PES. The selected MPW1K 28,42 (modified Perdew-Wang one-parameter model for kinetics) hybrid functional is based on the PerdewWang exchange functional with Adamo and Barone's modified enhancement factor and the Perdew-Wang correlation functional.…”

“…35, and in Figure 1 and the Supporting Information of ref. 37. The corresponding classical and adiabatic potential energies (i.e., including, the zero-point energy corrections) with respect to the reactants are given in Tables 1 and 2 of ref.…”

“…In previous theoretical studies, [37][38][39] we carried out ab initio and density functional electronic structure calculations of the most relevant stationary points and reactions pathways on the PES corresponding to the reaction process initiated by DMSÁOH 1 O 2 and leading to the formation of the DMSO product also in the presence of NO x . The reaction of O 2 with the DMSÁOH adduct initially leads to a reactant complex in the entrance region.…”

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

“…The main gas‐phase degradation process of DMS in the troposphere is chemical oxidation initiated by OH radicals during the day and by NO 3 radicals at night. These processes lead to the formation of sulfur‐containing species, such as sulfuric and methane sulfonic acids, which can significantly contribute to the acidity of the atmosphere 2–5. It has been postulated that emissions of DMS from the oceans may have a significant influence on the Earth's radiation budget and possibly in climate regulation due to the formation of CCN (cloud condensation nuclei) from the oxidation of SO 2 formed in the photo‐oxidation of DMS 6–10.…”