Kinetic Study on the Reaction of OH Radical with Dimethyl Sulfide in the Absence of Oxygen

Abstract

A variational transition-state theory calculation for the reaction of OH radical with dimethyl sulfide (DMS) in the absence of oxygen is presented. The potential energy surface was previously studied and the effects of different levels of theory were analyzed. Here we propose a kinetic model for the atmospheric DMS oxidation in the absence of oxygen. For the first time, addition of OH to DMS and CH(3)SOH elimination channels are connected, and the equilibrium approximation in the high-pressure regime is applied to the DMS-OH adduct in the absence of oxygen. Both low- and high-pressure limits are considered to analyze the two different mechanisms of the H-abstraction channel, and two different kinetic approaches are applied to study them. The rate constants for the addition-elimination and H-abstraction routes are compared and the branching ratios are also studied. Tunneling contributions and kinetic isotope effects are analyzed. We conclude, in agreement with experimental observations, that in the absence of oxygen DMS oxidation takes place via H-abstraction with a branching ratio of 1.0 at atmospheric temperatures.

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

“…The geometries of all the stationary points for reactions R1abs, R1add, R2a/R2b, and R3 are shown in Figure 1 of ref. 35, and in Figure 1 and the Supporting Information of ref. 37.…”

“…In this case, two H-abstraction saddle point structures, SPabs1-1 (SPabs1 in ref. 35) and SPabs1-2, and a minimum energy structure (MIN1) in between have been located on the MPW1K/MG3S MEP. The expectation values for S 2 before and after spin annihilation in the density functional theory (DFT) calculations are 0.78 and 0.76, respectively, and therefore, there is no spin contamination.…”

“…[29][30][31][32] In addition, some theoretical works [33][34][35] have been published concerning the kinetics of DMS 1 OH reaction in the absence of O 2 . In most of those theoretical studies, 35 the potential energy surface (PES) and the individual rate constants for the different channels of the DMS 1 OH reaction were calculated (addition-elimination and H-abstraction) as a function of temperature using canonical variational transition-state theory (CVT) and including tunneling corrections when needed. The H-abstraction channel was found dominant, and then the low-pressure and high-pressure limits were analyzed.…”

H-Abstraction from Dimethyl Sulfide in the Presence of an Excess of Hydroxyl Radicals. A Quantum Chemical Evaluation of Thermochemical and Kinetic Parameters Unveils an Alternative Pathway to Dimethyl Sulfoxide

“…Albu et al study 30 provided a rate coefficient at 298 K of (5.00 ± 1.00) x 10 -12 cm 3 molecule -1 s -1 in agreement with the previously mentioned best value recommended by Atkinson et al 27 . Later work by González-García et al 31 , following a previous idea of El-Nahas et al 32 , invoked the existence of two possible reaction channels for the decomposition, one through direct abstraction and another through indirect abstraction starting from a precursor complex (as postulated by Sekušak et al 33 ). Under this assumption, González-García et al 31 proposed that the reaction is not pressure independent (contrary to the experimental results of Hynes et al 7 ).…”

“…Later work by González-García et al 31 , following a previous idea of El-Nahas et al 32 , invoked the existence of two possible reaction channels for the decomposition, one through direct abstraction and another through indirect abstraction starting from a precursor complex (as postulated by Sekušak et al 33 ). Under this assumption, González-García et al 31 proposed that the reaction is not pressure independent (contrary to the experimental results of Hynes et al 7 ). They calculated that at low pressures the temperature dependence follows an Arrhenius behavior, while at high pressures the behavior is Arrhenius like only at higher temperatures, and reverse Arrhenius at lower ones.…”