Quantum chemical studies of hydrate formation of H2SO4 and HSO4

We calculate structures and thermochemical parameters for H 2 SO 4 ·(H 2 O) n , HSO 4 ·(H 2 O) n , H 2 SO 4 ·NH 3 ·(H 2 O) m and HSO 4 ·NH 3 ·(H 2 O) m clusters (with n = 0... 4 and m = 0... 1) using the MP2/aug-cc-pV(D + d)Z quantum chemical method, with higher-order corrections computed at the MP2/aug-cc-pV(T + d)Z and MP4/aug-cc-pV(D + d)Z levels. Equilibrium constants for hydrate formation at different temperatures are computed using the quantum chemical results, and the predicted extent of hydrate formation is compared with experimental results. Hydrate distributions in different RH conditions are derived using the calculated free energies of hydration. The results show that the hydrogensulfate ion is in all conditions much more strongly hydrated than the neutral sulfuric acid molecule. The high-level thermodynamic data calculated for the clusters agree with the experimental data, and the presented hydrate model is expected to perform better than earlier versions based on less reliable quantum chemical data. A comparison to the ammonia-containing clusters indicates that ammonia probably plays at most a minor role in ion-induced nucleation involving the HSO 4 - core ion.