Effect of a single water molecule on the HO 2 + ClO reaction

2018

Molecules

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Mechanism and kinetic studies have been carried out to investigate whether one and two water molecules could play a possible catalytic role on the CH2O + ClO reaction. Density functional theory combined with the coupled cluster theory were employed to explore the potential energy surface and the thermodynamics of this radical-molecule reaction. The reaction proceeded through four different paths without water and eleven paths with water, producing H + HCO(O)Cl, Cl + HC(O)OH, HCOO + HCl, and HCO + HOCl. Results indicate that the formation of HCO + HOCl is predominant both in the water-free and water-involved cases. In the absence of water, all the reaction paths proceed through the formation of a transition state, while for some reactions in the presence of water, the products were directly formed via barrierless hydrogen transfer. The rate constant for the formation of HCO + HOCl without water is 2.6 × 10−16 cm3 molecule−1 s−1 at 298.15 K. This rate constant is decreased by 9−12 orders of magnitude in the presence of water. The current calculations hence demonstrate that the CH2O + ClO reaction is impeded by water.

Section: Resultssupporting

confidence: 90%

The Role of (H2O)1-2 in the CH2O + ClO Gas-Phase Reaction

2018

Molecules

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“…In the presence of a single water molecule, both reactants are susceptible to form binary complexes with water via hydrogen bond or halogen bond interactions. , Through one of its hydrogen atoms, water clustered to DMS in one direction, exclusively, via a 2.4 Å hydrogen bond with the S atom of DMS to form DMS···H 2 O. It should be noted that this hydrogen bond with sulfur being longer than generally observed with oxygen is a result of a weaker interaction between the partial charge of the hydrogen atom and the dipole and quadrupole of the sulfur atom, as opposed to charge–charge interactions in hydrogen bonds with oxygen .…”

Section: Results and Discussionmentioning

confidence: 99%

“…The possible reactions inside the hydrated particles have aroused great interest among researchers. − The importance of water in atmospheric processes has always been concerned, but its role as a catalyst in chemical reactions is not completely elucidated and remains highly uncertain. Water could participate in atmospheric reactions by forming hydrogen bonds with reactive species, thereby having a decisive effect on their gas-phase chemistry. − The study of Vöhringer-Martinez et al was one of the first to elucidate that a single water molecule could catalyze the molecule–radical reactions involving OH . Aloisio and Francisco first proposed that the photochemical properties of molecule–water complexes are different from those of individual molecules .…”

Section: Introductionmentioning

confidence: 99%

Influence of Water on the Gas-Phase Reaction of Dimethyl Sulfide with BrO in the Marine Boundary Layer

Tang

et al. 2021

ACS Omega

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The effect of a single water molecule on the reaction of dimethyl sulfide (DMS) with BrO reaction has been investigated using quantum chemical calculations at the CCSD(T)/6-311++G**//BH&HLYP/aug-cc-pVTZ level of theory. Two reaction mechanisms have been considered both in the absence and the presence of water, namely, oxygen atom transfer and hydrogen abstraction, among which the oxygen atom transfer was predominant. Five reaction channels were found in the absence of water, in which the channels starting from the cis-configuration of the pre-reaction complexes were more favorable because of the low energy barrier. The inclusion of water slightly decreased the energy barrier height of most oxygen atom transfer channels, while making the hydrogen abstraction channels more complex. While the effective rate coefficients for the oxygen atom transfer paths are found to have decreased by 3–7 orders of magnitude in the presence of water relative to the water-free reactions, the negligible fraction of reactants that are effectively clustered with water does not significantly change the overall rate of the formation of dimethyl sulfoxide and Br. The present results show that the overall mechanism and rate of the DMS + BrO reaction may not be affected by humidity under atmospheric conditions.

“…Du and Zhang used the CCSD(T)/6-311++G(3df,3pd)//BH&HLYP/6-311++G(3df,3pd) method to calculate the rate coefficients for H 2 S and • OH reaction without and with catalyst X (X = H 2 O, (H 2 O) 2 , or H 2 S) by employing conventional transition-state theory, and they concluded that the presence of X would not play an important role in the oxidation of H 2 S by • OH radicals under atmospheric conditions . Some recent studies, however, showed inhibitive effects of water in hydrogen abstraction reactions involving ClO. − Interestingly, for the reaction of CH 3 OH + ClO, the effect of water was found to be much more negative on the formation of HOCl + CH 2 OH than on the formation of HOCl + CH 3 O . For the reaction between the HCOOH···H 2 O complex and the hydroxy radical, the rate coefficient was 4 times lower than that of the bared reaction .…”

Section: Introductionmentioning

confidence: 99%

Role of (H₂O)_n (n = 1–2) in the Gas-Phase Reaction of Ethanol with Hydroxyl Radical: Mechanism, Kinetics, and Products

Tang

et al. 2019

ACS Omega

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The effect of water on the hydrogen abstraction mechanism and product branching ratio of CH 3 CH 2 OH + • OH reaction has been investigated at the CCSD(T)/aug-cc-pVTZ//BH&HLYP/aug-cc-pVTZ level of theory, coupled with the reaction kinetics calculations, implying the harmonic transition-state theory. Depending on the hydrogen sites in CH 3 CH 2 OH, the bared reaction proceeds through three elementary paths, producing CH 2 CH 2 OH, CH 3 CH 2 O, and CH 3 CHOH and releasing a water molecule. Thermodynamic and kinetic results indicate that the formation of CH 3 CHOH is favored over the temperature range of 216.7–425.0 K. With the inclusion of water, the reaction becomes quite complex, yielding five paths initiated by three channels. The products do not change compared with the bared reaction, but the preference for forming CH 3 CHOH drops by up to 2%. In the absence of water, the room temperature rate coefficients for the formation of CH 2 CH 2 OH, CH 3 CH 2 O, and CH 3 CHOH are computed to be 5.2 × 10 –13 , 8.6 × 10 –14 , and 9.0 × 10 –11 cm 3 molecule –1 s –1 , respectively. The effective rate coefficients of corresponding monohydrated and dihydrated reactions are 3–5 and 6–8 orders of magnitude lower than those of the unhydrated reaction, indicating that water has a decelerating effect on the studied reaction. Overall, the characterized effects of water on the thermodynamics, kinetics, and products of the CH 3 CH 2 OH + • OH reaction will facilitate the understanding of the fate of ethanol and secondary pollutants derived from it.