The reaction mechanism of SO3 with the multifunctional compound ethanolamine and its atmospheric implications.

SO₃ is an important reactive species in sulfur cycle and sulfuric acid formation processes and its reactions with some functional group substances, such as H₂O, NH₃, CH₃OH, and organic and inorganic acids, have been extensively studied. However, its loss mechanism with multifunctional species is still lacking in detail. Herein, the reaction mechanism between SO3 and monoethanolamide (MEA) was investigated in the gas phase and on water droplets. The quantum chemical calculations indicate that the gas-phase reactions of SO₃ with the OH and NH₂ moieties of MEA hardly occur as their reaction energy barriers are up to 21.9-29.4 kcal mol-1. When a single water molecule is added into the SO₃ + MEA reaction, it not only decreases the reaction barrier by at least 15.0 kcal mol-1 and thus enhances the rate obviously, but can also lead to the main product changing from HOCH₂CH₂NHSO₃H to NH₂CH₂CH₂OSO₃H. The Born Oppenheimer molecular dynamics simulations on a water droplet show that the routes of the NH₂CH₂CH₂OSO₃- ··· H₃O+ ion pair, HSO4 - and HOCH₂CH₂NH₃ + ions and zwitterionic formations of HOCH₂CH₂NH₂ +-SO₃ - and SO₃ --OCH₂CH₂NH₃ + occur through a loopstructure route or chain reaction process, and can be finished within several picoseconds. Interestingly, the nucleation simulations show that the products of HOCH₂CH₂NHSO₃H and NH₂CH₂CH₂OSO₃H have a potential ability to participate in the formation of new particles as they can form larger clusters with H₂SO4, NH₃ and H₂O molecules within 20 ns. Thus, the present study will not only give new insight into the reaction between SO₃ and multifunctional compounds, but also provide a new potential formation mechanism for particles resulting from the loss of SO₃. [ABSTRACT FROM AUTHOR]