Atmospheric ozonolysis of allyl sulfides: Theoretical and experimental study of kinetics and product yields in the presence and absence of an OH radical scavenger

Abstract

This work presents an experimental and computational study of the ozonolysis of allyl methyl sulfide (H₂C=CHCH₂SCH₃, AMS) and allyl ethyl sulfide (H₂C=CHCH₂SCH₂CH₃, AES) in the gas phase at atmospheric conditions. The experiments were carried out using carbon monoxide (CO) as scavengers of nascent OH radicals. The main products of the reaction with O₃ from AMS and AES were identified and quantified by in situ FTIR spectroscopy. The yields of the SO₂, formaldehyde and formic acid products found were (26 ± 1) %, (62 ± 1) % and (7 ± 1) % for the AMS/CO/O₃ reaction, and (19 ± 1) %, (62 ± 1) % and (8 ± 1) % for the AES/CO/O₃ reaction, respectively. Besides those products, acrolein was also identified when the OH radical scavenger was absent. In this case, the yields obtained were (37 ± 1) %, (6 ± 1) %, (63 ± 1) % and (4 ± 1) % in the AMS/O₃ mixture, and (28 ± 1) %, (5 ± 1) %, (41 ± 1) % and (4 ± 1) % in the AES/O₃ mixture, for SO₂, acrolein, formaldehyde and formic acid, respectively. A small difference in product yields in the presence of CO could be attributed to secondary reactions with OH radicals.

DFT and post-Hartree-Fock composite computational chemistry calculations of reactants, transition states and products in the reaction paths were used to lend support to the experimental findings for the AMS + O₃ reaction. The calculated rate coefficients obtained in this work are in close agreement with the experimental data, with the ωB97X-D3(BJ)/aug-cc-pVTZ and ωB97X-V/aug-cc-pVTZ as the most accurate and reliable DFT methods. The inclusion of the SVECV-f12 protocol on top of those DFT calculations markedly improves the accuracy of the results. Atmospheric implications are discussed in terms of significant POCP and AP of sulfides and its products obtained.