Competition Between H₂SO₄–(CH₃)₃N and H₂SO₄–H₂O Interactions: Theoretical Studies on the Clusters [(CH₃)₃N]·(H₂SO₄)·(H₂O)_3–7

The role of the nucleation of sulfuric acid with amines in aerosol formation and its implications for environment is one of the fundamental unsettled questions in atmospheric chemistry. We have investigated the cluster of [(CH₃)₃N]·(H₂SO₄)·(H₂O)_<i>n</i> (<i>n</i> = 3–7) by molecular dynamics to obtain configurational sampling combination with CAM-B3LYP/6-311G­(d,p) level to locate the global and many local minima for each cluster size. According to the binding energies at the method of MP2/6-311++G­(d,p), the total binding energies decrease with the increasing of the water molecules. For each global minimum, the average binding energies decrease from <i>n</i> = 3 to 4, then increase slowly. The protons of H₂SO₄ are preferred to transfer to the (CH₃)₃N to form ion-pair HSO₄^– and (CH₃)₃NH⁺, and the (CH₃)₃NH⁺ ions are coordinated at the first hydrated shell of HSO₄^– when <i>n</i> is between 3 and 5 and coordinated at the second or third hydrated shell when <i>n</i> is larger than 5