The reaction mechanism of SO 3 with the multifunctional compound ethanolamine and its atmospheric implications.

SO 3 is an important reactive species in sulfur cycle and sulfuric acid formation processes and its reactions with some functional group substances, such as H 2 O, NH 3 , CH 3 OH, 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 SO 3 and monoethanolamide (MEA) was investigated in the gas phase and on water droplets. The quantum chemical calculations indicate that the gas-phase reactions of SO 3 with the OH and NH 2 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 SO 3 + 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 HOCH 2 CH 2 NHSO 3 H to NH 2 CH 2 CH 2 OSO 3 H. The Born Oppenheimer molecular dynamics simulations on a water droplet show that the routes of the NH 2 CH 2 CH 2 OSO 3 - ⋯H 3 O + ion pair, HSO 4 - and HOCH 2 CH 2 NH 3 + ions and zwitterionic formations of HOCH 2 CH 2 NH 2 + -SO 3 - and SO 3 - -OCH 2 CH 2 NH 3 + occur through a loop-structure route or chain reaction process, and can be finished within several picoseconds. Interestingly, the nucleation simulations show that the products of HOCH 2 CH 2 NHSO 3 H and NH 2 CH 2 CH 2 OSO 3 H have a potential ability to participate in the formation of new particles as they can form larger clusters with H 2 SO 4 , NH 3 and H 2 O molecules within 20 ns. Thus, the present study will not only give new insight into the reaction between SO 3 and multifunctional compounds, but also provide a new potential formation mechanism for particles resulting from the loss of SO 3 .