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A study of the thermodynamics and mechanisms of the atmospherically relevant reaction dimethyl sulphide (DMS) with atomic chlorine (Cl) in the absence and presence of water, using electronic structure methods

A study of the thermodynamics and mechanisms of the atmospherically relevant reaction dimethyl sulphide (DMS) with atomic chlorine (Cl) in the absence and presence of water, using electronic structure methods
A study of the thermodynamics and mechanisms of the atmospherically relevant reaction dimethyl sulphide (DMS) with atomic chlorine (Cl) in the absence and presence of water, using electronic structure methods

The thermodynamics and mechanisms of the atmospherically relevant reaction dimethyl sulphide (DMS) + atomic chlorine (Cl) were investigated in the absence and presence of a single water molecule, using electronic structure methods. Stationary points on each reaction surface were located using density functional theory (DFT) with the M06-2X functional with aug-cc-pVDZ (aVDZ) and aug-cc-pVTZ (aVTZ) basis sets. Then fixed point calculations were carried out using the UM06-2X/aVTZ optimised stationary point geometries, with aug-cc-pVnZ basis sets (n = T and Q), using the coupled cluster method [CCSD(T)], as well as the domain-based local pair natural orbitals coupled cluster [DLPNO-UCCSD(T)] approach. Four reaction channels are possible, formation of (A) CH3SCH2 + HCl, (B) CH3S + CH3Cl, (C) CH3SCl + CH3, and (C′) CH3S(Cl)CH3. The results show that, in the absence of water, channels A and C′ are the dominant channels. In the presence of water, the calculations show that the reaction mechanisms for A and C formation change significantly. Channel A occurs via submerged TSs and is expected to be rapid. Channel B occurs via TSs which present significant energy barriers indicating that this channel is not significant in the presence of water relative to CH3SCH2 + HCl and DMS·Cl adduct formation, as is the case in the absence of water. Channel C was not considered as it is endothermic in the absence of water. In the presence of water, pathways which proceed via (a) DMS·H2O + Cl, (b) Cl·H2O + DMS and (c) DMS·Cl + H2O were considered. It was found that under tropospheric conditions, reactions via pathway (b) are of minor importance relative to those that proceed via pathways (a) and (c). This study has shown that water changes the mechanisms of the DMS + Cl reactions significantly but the presence of water is not expected to affect the overall reaction rate coefficient under atmospheric conditions as the DMS + Cl reaction has a rate coefficient at room temperature close to the collisional limit.

1463-9076
4780-4793
Rhyman, Lydia
d025e9f5-e723-49fd-ad1c-0a0508e6eb8a
Lee, Edmond P.F.
c54ce72b-3148-46ac-83fd-2d83d23d485f
Ramasami, Ponnadurai
5401f300-4ad3-4d35-8762-822768d6bd0c
Dyke, John M.
46393b45-6694-46f3-af20-d7369d26199f
Rhyman, Lydia
d025e9f5-e723-49fd-ad1c-0a0508e6eb8a
Lee, Edmond P.F.
c54ce72b-3148-46ac-83fd-2d83d23d485f
Ramasami, Ponnadurai
5401f300-4ad3-4d35-8762-822768d6bd0c
Dyke, John M.
46393b45-6694-46f3-af20-d7369d26199f

Rhyman, Lydia, Lee, Edmond P.F., Ramasami, Ponnadurai and Dyke, John M. (2023) A study of the thermodynamics and mechanisms of the atmospherically relevant reaction dimethyl sulphide (DMS) with atomic chlorine (Cl) in the absence and presence of water, using electronic structure methods. Physical Chemistry Chemical Physics, 25 (25), 4780-4793. (doi:10.1039/d2cp05814f).

Record type: Article

Abstract

The thermodynamics and mechanisms of the atmospherically relevant reaction dimethyl sulphide (DMS) + atomic chlorine (Cl) were investigated in the absence and presence of a single water molecule, using electronic structure methods. Stationary points on each reaction surface were located using density functional theory (DFT) with the M06-2X functional with aug-cc-pVDZ (aVDZ) and aug-cc-pVTZ (aVTZ) basis sets. Then fixed point calculations were carried out using the UM06-2X/aVTZ optimised stationary point geometries, with aug-cc-pVnZ basis sets (n = T and Q), using the coupled cluster method [CCSD(T)], as well as the domain-based local pair natural orbitals coupled cluster [DLPNO-UCCSD(T)] approach. Four reaction channels are possible, formation of (A) CH3SCH2 + HCl, (B) CH3S + CH3Cl, (C) CH3SCl + CH3, and (C′) CH3S(Cl)CH3. The results show that, in the absence of water, channels A and C′ are the dominant channels. In the presence of water, the calculations show that the reaction mechanisms for A and C formation change significantly. Channel A occurs via submerged TSs and is expected to be rapid. Channel B occurs via TSs which present significant energy barriers indicating that this channel is not significant in the presence of water relative to CH3SCH2 + HCl and DMS·Cl adduct formation, as is the case in the absence of water. Channel C was not considered as it is endothermic in the absence of water. In the presence of water, pathways which proceed via (a) DMS·H2O + Cl, (b) Cl·H2O + DMS and (c) DMS·Cl + H2O were considered. It was found that under tropospheric conditions, reactions via pathway (b) are of minor importance relative to those that proceed via pathways (a) and (c). This study has shown that water changes the mechanisms of the DMS + Cl reactions significantly but the presence of water is not expected to affect the overall reaction rate coefficient under atmospheric conditions as the DMS + Cl reaction has a rate coefficient at room temperature close to the collisional limit.

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Accepted/In Press date: 17 January 2023
e-pub ahead of print date: 18 January 2023
Additional Information: Funding Information: This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number OCI-1053575. LR and PR would also like to acknowledge computing facilities from the Centre for High Performance Computing of South Africa. LR also acknowledges the postdoctoral fellowship from the Higher Education Commission (formerly known as Tertiary Education Commission) of Mauritius.

Identifiers

Local EPrints ID: 475556
URI: http://eprints.soton.ac.uk/id/eprint/475556
ISSN: 1463-9076
PURE UUID: 715bb666-6365-4ae3-9ce6-8fcf6db7992f
ORCID for John M. Dyke: ORCID iD orcid.org/0000-0002-9808-303X

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Date deposited: 21 Mar 2023 17:42
Last modified: 18 Mar 2024 02:32

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Contributors

Author: Lydia Rhyman
Author: Edmond P.F. Lee
Author: Ponnadurai Ramasami
Author: John M. Dyke ORCID iD

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