Ab initio study of gas-phase sulphuric acid hydrates containing 1 to 3 water molecules

Abstract

Sulphuric acid has a tendency to form hydrates, small clusters containing a few water molecules, in the gas phase. Hydrate formation has a stabilising effect on the vapour as the pressure of sulphuric acid drops (relative to unhydrated vapor), decreasing the nucleation rate. In classical nucleation theories the hydration energies and the hydrate distribution are predicted assuming that hydrates can be described as liquid droplets having thermodynamic properties of bulk liquid. To obtain a better understanding of the structures and formation energies of the smallest clusters, we have performed ab initio density functional calculations of the mono-,di-, and trihydrates. The hydrogen bonds between the molecules are found to be strong. The more water molecules the hydrate contains, the clearer ring-like structure is formed. Comparison to classical values for the hydration enthalpies confirms that the properties of bulk liquid do not describe the properties of the smallest clusters too well. The energy barrier for proton transfer reaction H2SO4⋅H2O →HSO4−⋅H3O+ for mono- and dihydrate is high, and protonisation is unlikely to occur, but in trihydrate the protonisation has almost occurred and the barrier is very low. We also studied the singly protonised monohydrate, and found that while sulphuric acid forms H bonds with the OH parts, the hydrogen sulphate ion tends to bind with the O (S=O) part, and the second proton stays tightly in the ion.

Toward elimination of discrepancies between theory and experiment: The rate constant of the atmospheric conversion of SO 3 to H 2 SO 4

“…We did not find evidence for any ionic character of the 1:1 and also 1:2 sulfuric acid-water minima, which also agrees with the experimental (82) and theoretical findings (84). On the other hand, the global minimum we find for the 1:2 complex differs from the one assumed in the literature to be the global minimum (81). The cyclic arrangement of the two water molecules around sulfuric acid we find here is favorable by 3.28 kcal͞mol over the double chain structure noted in the literature.…”

Switching Supramolecular Polymeric Materials with Multiple Length Scales

“…Because of the large absorption bandwidth of the sulfonate regime, F TIR does not easily lend itself to detailed investigation of such hydrogen bonding. However, calculations of hydrogen-bonded complexes of sulfuric acid and water (13) suggest that the hydrogen bonding between the phenolic hydroxyl group and the sulfonate group of MSA becomes energetically feasible once a proton has been transferred from MSA to P4VP. Thus, the expected supramolecular structure combines proton transfer and hydrogen bonding (Scheme 1).…”

Investigating Atmospheric Sulfuric Acid–Water–Ammonia Particle Formation Using Quantum Chemistry

“…Relevant hydrates contain only 1-5 water molecules and one sulfuric acid molecule, and thus they are small enough to be treated with quantum chemical methods. Several groups have studied the structure and energetics of different protolysis states of the small hydrates [38,44,47,[52][53][54][55][56]. Although hydrates with two sulfuric acid molecules contain a negligible fraction of the total gas-phase sulfuric acid, they are important for the nucleation process, as the critical clusters (at least in pure sulfuric acid-water nucleation) probably contain more than one sulfuric acid molecule, and they have also been the focus of several studies [56][57][58].…”