Two sulfuric acids in small water clusters

We have studied clusters containing two sulfuric acid (SA) molecules and 0-8 water molecules using density functional methods. Our main interest was to study the energies and structures of the formed clusters. We are interested in the SA-assisted nucleation of water, and the formation free energies of the clusters will help to understand the first steps of this process. Also, the deprotonation of SA is interesting. For single SA, the first deprotonations happen when three waters are present. Here, the second SA will replace the water, and the deprotonation will happen when two waters are present. The second SA will deprotonate in clusters containing four waters. At the larger cluster (n = 5-8) both of the acids are singly deprotonated. We did not observe any doubly deprotonated sulfuric acids, SO42-. We also obtained several stable structures of these clusters. The most stable structures contain solvent separated acid-hydronium ion pairs whenever it is was possible.